Video region partition based on color format

ABSTRACT

A method of video processing is provided to include: determining a partitioning scheme for partitioning a chroma video region of a video into one or more chroma blocks based on a color format of the video according to a rule; and performing a conversion between the video and a coded representation of the video according to the partitioning scheme.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2020/107381, filed on Aug. 6, 2020, which claims the priorityto and benefit of International Patent Application No.PCT/CN2019/099447, filed on Aug. 6, 2019. For all purposes under thelaw, the entire disclosure of the aforementioned applications isincorporated by reference as part of the disclosure of this application.

TECHNICAL FIELD

This document is related to video and image coding and decodingtechnologies.

BACKGROUND

Digital video accounts for the largest bandwidth use on the internet andother digital communication networks. As the number of connected userdevices capable of receiving and displaying video increases, it isexpected that the bandwidth demand for digital video usage will continueto grow.

SUMMARY

The disclosed techniques may be used by video or image decoder orencoder embodiments for in which reference pictures are used in videocoding or decoding.

In one example aspect a method of video processing is disclosed. Themethod includes determining a partitioning scheme for partitioning achroma video region of a video into one or more chroma blocks based on acolor format of the video according to a rule; and performing aconversion between the video and a coded representation of the videoaccording to the partitioning scheme.

In another example aspect, another method of video processing isdisclosed. The method includes determining prediction modes orprediction types for subblocks of a coding tree node of a video based ona color format of the video; and performing a conversion between thevideo and a coded representation of the video based on the determining,wherein the coding tree node is partitioned into the subblocks forcoding in the coded representation.

In another example aspect, another method of video processing isdisclosed. The method includes performing a conversion between a videocomprising one or more video regions comprising one or more luma blocksand one or more chroma blocks and a coded representation of the videoaccording to a rule; wherein the rule specifies that a chroma block fromthe one or more chroma blocks having a size M×N is disallowed to berepresented in the coded representation using an intra mode or an intrablock copy mode, wherein M and N are integers that indicate a width anda height of the chroma block, respectively; wherein the intra modeincludes encoding the chroma block based on previously encoded orreconstructed video blocks, and wherein the intra block copy modeincludes encoding the chroma block using at least a block vectorpointing to a video frame containing a video region.

In another example aspect, another method of video processing isdisclosed. The method includes determining, for a conversion between avideo region of a video and a coded representation of the video, to usea combined inter and intra prediction (CIIP) mode as an intra mode or aninter mode according to a rule; and performing the conversion based onthe determining, and wherein the CIIP mode include combining an intraprediction signal and a inter prediction signal using weightedcoefficients.

In another example aspect, another method of video processing isdisclosed. The method includes performing a conversion between a chromablock of a video and a coded representation of the video, wherein thechroma block is represented in the coded representation using an intracoding mode according to a size rule; wherein the size rule specifiesthat the intra coding mode is from a first set of intra coding modetypes, in case that a width of the chroma block is equal to M or aheight of the chroma block is equal to N, where M and N are integers;otherwise the intra coding mode is from a second set of intra codingmode types.

In another example aspect, another method of video processing isdisclosed. The method includes performing a conversion between a chromablock of a video and a coded representation of the video, wherein thechroma block is represented in the coded representation using atransform type according to a rule; wherein the rule specifies that thetransform type is from a first set of transform types in case that awidth of the chroma block is equal to M or a height of the chroma blockis equal to N, where M and N are integers; otherwise the transform typeis from a second set of transform types.

In another example aspect, another method of video processing isdisclosed. The method includes performing a conversion between a videocomprising a video region having one or more luma blocks and one or morechroma blocks and a coded representation of the video according to arule, wherein the rule specifies that use of an intra block copy (IBC)mode is available for the one or more luma blocks and the one or morechroma blocks having a block size M×N, for all values of M and N, whereM and N are integers; wherein, using the IBC mode, a video block iscoded using at least a block vector pointing to a video frame containingthe video block.

In another example aspect, another method of video processing isdisclosed. The method includes performing a conversion between a videoblock of a video and a coded representation of the video block, whereinthe coded representation conforms to a formatting rule, wherein theformatting rule specifies a selective inclusion of a syntax elementindicative of use of an inter block copy (IBC) mode in the codedrepresentation based on a mode type of the video block, and wherein theIBC mode includes encoding the video block using at least a block vectorpointing to a video frame containing the video block.

In another example aspect, another method of video processing isdisclosed. The method includes performing a conversion between a videoblock of a video and a coded representation of the video block, whereinthe coded representation conforms to a formatting rule, wherein theformatting rule specifies that a syntax element indicative of use of apalette mode is included in the coded representation regardless of amode type of the video block, and wherein the pallet mode includesencoding the video block using a palette of representative samplevalues.

In another example aspect, another method of video processing isdisclosed. The method includes determining, for a conversion between avideo region of a video and a coded representation of the video, basedon a rule, that use of an inter block copy (IBC) mode is permitted forthe video region; and performing the conversion based on thedetermining, wherein the IBC mode includes encoding the video regionusing at least a block vector pointing to a video frame containing thevideo region.

In another example aspect, another method of video processing isdisclosed. The method includes determining, for a conversion between avideo region of a video and a coded representation of the video, basedon a rule, whether use of a palette mode is permitted for the videoregion; and performing the conversion based on the determining, whereinthe rule is based on a coding mode type of the video region or a colortype of the video region, and wherein the palette mode includes encodingthe video region using a palette of representative sample values.

In yet another example aspect, the above-described method may beimplemented by a video encoder apparatus that comprises a processor.

In yet another example aspect, the above-described method may beimplemented by a video decoder apparatus that comprises a processor.

In yet another example aspect, these methods may be embodied in the formof processor-executable instructions and stored on a computer-readableprogram medium.

These, and other, aspects are further described in the present document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of intra block copy coding tool.

FIG. 2 shows an example of a block coded in palette mode.

FIG. 3 shows an example of use of palette predictor to signal paletteentries.

FIG. 4 shows an example of examples of Horizontal and vertical traversescans.

FIG. 5 shows examples of coding of palette indices.

FIG. 6 shows an example of 67 intra prediction modes.

FIG. 7 shows examples of the left and above neighbours of the currentblock.

FIG. 8 shows examples of ALF filter shapes (chroma: 5×5 diamond, luma:7×7 diamond).

FIG. 9 shows an example of subsampled Laplacian calculation.

FIG. 10 shows an example of a modified block classification at virtualboundaries.

FIG. 11 is an example illustration of modified ALF filtering for Lumacomponent at virtual boundaries.

FIG. 12 shows examples of four 1-D 3-pixel patterns for the pixelclassification in EO.

FIG. 13 shows that four bands are grouped together and represented byits starting band position.

FIG. 14 shows top and left neighboring blocks used in CIIP weightderivation.

FIG. 15 shows Luma mapping with chroma scaling architecture.

FIG. 16 shows examples of SCIPU.

FIGS. 17A and 17B are block diagrams of examples of a hardware platformused for implementing techniques described in the present document.

FIG. 18 is a flowchart for an example method of video processing.

FIG. 19 shows examples of positions of spatial merge candidates.

FIG. 20 shows examples of candidate pairs considered for redundancycheck of spatial merge candidates.

FIGS. 21A and 21B show flowcharts for example methods of videoprocessing based on some implementations of the disclosed technology.

FIGS. 22A and 22B show flowcharts for example methods of videoprocessing based on some implementations of the disclosed technology.

FIGS. 23A and 23B show flowcharts for example methods of videoprocessing based on some implementations of the disclosed technology.

DETAILED DESCRIPTION

The present document provides various techniques that can be used by adecoder of image or video bitstreams to improve the quality ofdecompressed or decoded digital video or images. For brevity, the term“video” is used herein to include both a sequence of pictures(traditionally called video) and individual images. Furthermore, a videoencoder may also implement these techniques during the process ofencoding in order to reconstruct decoded frames used for furtherencoding.

Section headings are used in the present document for ease ofunderstanding and do not limit the embodiments and techniques to thecorresponding sections. As such, embodiments from one section can becombined with embodiments from other sections.

1. Summary

This document is related to video coding technologies. Specifically, itis related to palette coding with employing base colors basedrepresentation in video coding. It may be applied to the existing videocoding standard like HEVC, or the standard (Versatile Video Coding) tobe finalized. It may be also applicable to future video coding standardsor video codec.

2. Initial Discussion

Video coding standards have evolved primarily through the development ofthe well-known ITU-T and ISO/IEC standards. The ITU-T produced H.261 andH.263, ISO/IEC produced MPEG-1 and MPEG-4 Visual, and the twoorganizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, thevideo coding standards are based on the hybrid video coding structurewherein temporal prediction plus transform coding are utilized. Toexplore the future video coding technologies beyond HEVC, Joint VideoExploration Team (JVET) was founded by VCEG and MPEG jointly in 2015.Since then, many new methods have been adopted by JVET and put into thereference software named Joint Exploration Model (JEM). In April 2018,the Joint Video Expert Team (JVET) between VCEG (Q6/16) and ISO/IEC JTC1SC29/WG11 (MPEG) was created to work on the VVC standard targeting at50% bitrate reduction compared to HEVC.

The latest version of VVC draft, i.e., Versatile Video Coding (Draft 4)could be found at:

http://phenix.it-sudparis.eu/jvet/doc_end_user/current_document.php?id=5755

The latest reference software of VVC, named VTM, could be found at:https://vcgit.hhi.fraunhofer.de/jvet/VVCSoftware_VTM/tags/VTM-5.0

2.1 Intra Block Copy

Intra block copy (IBC), a.k.a. current picture referencing, has beenadopted in HEVC Screen Content Coding extensions (HEVC-SCC) and thecurrent VVC test model (VTM-4.0). IBC extends the concept of motioncompensation from inter-frame coding to intra-frame coding. Asdemonstrated in FIG. 1 , the current block is predicted by a referenceblock in the same picture when IBC is applied. The samples in thereference block must have been already reconstructed before the currentblock is coded or decoded. Although IBC is not so efficient for mostcamera-captured sequences, it shows significant coding gains for screencontent. The reason is that there are lots of repeating patterns, suchas icons and text characters in a screen content picture. IBC can removethe redundancy between these repeating patterns effectively. InHEVC-SCC, an inter-coded coding unit (CU) can apply IBC if it choosesthe current picture as its reference picture. The MV is renamed as blockvector (BV) in this case, and a BV always has an integer-pixelprecision. To be compatible with main profile HEVC, the current pictureis marked as a “long-term” reference picture in the Decoded PictureBuffer (DPB). It should be noted that similarly, in multiple view/3Dvideo coding standards, the inter-view reference picture is also markedas a “long-term” reference picture.

Following a BV to find its reference block, the prediction can begenerated by copying the reference block. The residual can be got bysubtracting the reference pixels from the original signals. Thentransform and quantization can be applied as in other coding modes.

FIG. 1 is an illustration of Intra block copy.

However, when a reference block is outside of the picture, or overlapswith the current block, or outside of the reconstructed area, or outsideof the valid area restricted by some constrains, part or all pixelvalues are not defined. Basically, there are two solutions to handlesuch a problem. One is to disallow such a situation, e.g. in bitstreamconformance. The other is to apply padding for those undefined pixelvalues. The following sub-sessions describe the solutions in detail.

2.2 IBC in HEVC Screen Content Coding Extensions

In the screen content coding extensions of HEVC, when a block usescurrent picture as reference, it should guarantee that the wholereference block is within the available reconstructed area, as indicatedin the following spec text:

The variables offsetX and offsetY are derived as follows:

$\begin{matrix}{{offsetX} = {{\left( {{ChromaArrayType}\;==0} \right)\;?\; 0}\text{:}\mspace{14mu}\left( {{{{mvCLX}\lbrack 0\rbrack}\&}0x\;{7\;?\; 2}\text{:}0} \right)}} & \left( {8\text{-}104} \right) \\{{offsetY} = {{\left( {{ChromaArrayType}\;==0} \right)\;?\; 0}\text{:}\mspace{14mu}\left( {{{{mvCLX}\lbrack 0\rbrack}\&}0x\;{7\;?\; 2}\text{:}0} \right)}} & \left( {8\text{-}105} \right)\end{matrix}$It is a requirement of bitstream conformance that when the referencepicture is the current picture, the luma motion vector mvLX shall obeythe following constraints:

-   -   When the derivation process for z-scan order block availability        as specified in clause 6.4.1 is invoked with (xCurr, yCurr) set        equal to (xCb, yCb) and the neighbouring luma location (xNbY,        yNbY) set equal to (xPb+(mvLX[0]>>2)−offsetX,        yPb+(mvLX[1]>>2)−offsetY) as inputs, the output shall be equal        to TRUE.    -   When the derivation process for z-scan order block availability        as specified in clause 6.4.1 is invoked with (xCurr, yCurr) set        equal to (xCb, yCb) and the neighbouring luma location (xNbY,        yNbY) set equal to (xPb+(mvLX[0]>>2)+nPbW−1+offsetX,        yPb+(mvLX[1]>>2)+nPbH−1+−offsetY) as inputs, the output shall be        equal to TRUE.    -   One or both of the following conditions shall be true:        -   The value of (mvLX[0]>>2)+nPbW+xB1+offsetX is less than or            equal to 0.        -   The value of (mvLX[1]>>2)+nPbH+xB1+offsetY is less than or            equal to 0.    -   The following condition shall be true:

$\begin{matrix}{{{\left( {{xPb} + \left( {{{mvLX}\lbrack 0\rbrack}\operatorname{>>}2} \right) + {nPbSw} - 1 + {offsetX}} \right)/{CtbSizeY}} - {{xCb}/{CtbSizeY}}}<={{{yCB}/{CtbSizeY}} - {\left( {{yPb} + \left( {{{mvLX}\lbrack 1\rbrack}\operatorname{>>}\; 2} \right) + {nPbSh} - 1 + {offsetY}} \right)/{CtbSizeY}}}} & \left( {8\text{-}106} \right)\end{matrix}$

Thus, the case that the reference block overlaps with the current blockor the reference block is outside of the picture will not happen. Thereis no need to pad the reference or prediction block.

2.3 IBC in VVC Test Model

In the current VVC test model, i.e. VTM-4.0 design, the whole referenceblock should be with the current coding tree unit (CTU) and does notoverlap with the current block. Thus, there is no need to pad thereference or prediction block. The IBC flag is coded as a predictionmode of the current CU. Thus, there are totally three prediction modes,MODE_INTRA, MODE_INTER and MODE_IBC for each CU.

2.3.1 IBC Merge Mode

In IBC merge mode, an index pointing to an entry in the IBC mergecandidates list is parsed from the bitstream. The construction of theIBC merge list can be summarized according to the following sequence ofsteps:

-   -   Step 1: Derivation of spatial candidates    -   Step 2: Insertion of HMVP candidates    -   Step 3: Insertion of pairwise average candidates

In the derivation of spatial merge candidates, a maximum of four mergecandidates are selected among candidates located in the positionsdepicted in FIG. 19 . The order of derivation is A₁, B₁, B₀, A₀ and B₂.Position B₂ is considered only when any PU of position A₁, B₁, B₀, A₀ isnot available (e.g. because it belongs to another slice or tile) or isnot coded with IBC mode. After candidate at position A₁ is added, theinsertion of the remaining candidates is subject to a redundancy checkwhich ensures that candidates with same motion information are excludedfrom the list so that coding efficiency is improved. To reducecomputational complexity, not all possible candidate pairs areconsidered in the mentioned redundancy check. Instead only the pairslinked with an arrow in FIG. 20 are considered and a candidate is onlyadded to the list if the corresponding candidate used for redundancycheck has not the same motion information.

After insertion of the spatial candidates, if the IBC merge list size isstill smaller than the maximum IBC merge list size, IBC candidates fromHMVP table may be inserted. Redundancy check are performed wheninserting the HMVP candidates.

Finally, pairwise average candidates are inserted into the IBC mergelist.

When a reference block identified by a merge candidate is outside of thepicture, or overlaps with the current block, or outside of thereconstructed area, or outside of the valid area restricted by someconstrains, the merge candidate is called invalid merge candidate.

It is noted that invalid merge candidates may be inserted into the IBCmerge list.

2.3.2 IBC AMVP Mode

In IBC AMVP mode, an AMVP index point to an entry in the IBC AMVP listis parsed from the bitstream. The construction of the IBC AMVP list canbe summarized according to the following sequence of steps:

-   -   Step 1: Derivation of spatial candidates        -   Check A₀, A₁ until an available candidate is found.        -   Check B₀, B₁, B₂ until an available candidate is found.    -   Step 2: Insertion of HMVP candidates    -   Step 3: Insertion of zero candidates

After insertion of the spatial candidates, if the IBC AMVP list size isstill smaller than the maximum IBC AMVP list size, IBC candidates fromHMVP table may be inserted.

Finally, zero candidates are inserted into the IBC AMVP list.

2.4 Palette Mode

The basic idea behind a palette mode is that the samples in the CU arerepresented by a small set of representative colour values. This set isreferred to as the palette. And it is also possible to indicate a samplethat is outside the palette by signalling an escape symbol followed by(possibly quantized) component values. This kind of sample is calledescape sample. The palette mode is illustrated in FIG. 2 .

FIG. 2 shows an example of a block coded in palette mode.

2.5 Palette Mode in HEVC Screen Content Coding Extensions (HEVC-SCC)

In the palette mode in HEVC-SCC, a predictive way is used to code thepalette and index map.

2.5.1 Coding of the Palette Entries

For coding of the palette entries, a palette predictor is maintained.The maximum size of the palette as well as the palette predictor issignalled in the SPS. In HEVC-SCC, apalette_predictor_initializer_present_flag is introduced in the PPS.When this flag is 1, entries for initializing the palette predictor aresignalled in the bitstream. The palette predictor is initialized at thebeginning of each CTU row, each slice and each tile. Depending on thevalue of the palette_predictor_initializer_present_flag, the palettepredictor is reset to 0 or initialized using the palette predictorinitializer entries signalled in the PPS. In HEVC-SCC, a palettepredictor initializer of size 0 was enabled to allow explicit disablingof the palette predictor initialization at the PPS level.

For each entry in the palette predictor, a reuse flag is signalled toindicate whether it is part of the current palette. This is illustratedin FIG. 3 . The reuse flags are sent using run-length coding of zeros.After this, the number of new palette entries are signalled usingexponential Golomb code of order 0. Finally, the component values forthe new palette entries are signalled.

FIG. 3 shows an example of use of palette predictor to signal paletteentries.

2.5.2 Coding of Palette Indices

The palette indices are coded using horizontal and vertical traversescans as shown in FIG. 4 . The scan order is explicitly signalled in thebitstream using the palette_transpose_flag. For the rest of thesubsection it is assumed that the scan is horizontal.

FIG. 4 shows examples of Horizontal and vertical traverse scans.

The palette indices are coded using two main palette sample modes:‘INDEX’ and ‘COPY_ABOVE’. As explained previously, the escape symbol isalso signalled as an ‘INDEX’ mode and assigned an index equal to themaximum palette size. The mode is signalled using a flag except for thetop row or when the previous mode was ‘COPY_ABOVE’. In the ‘COPY_ABOVE’mode, the palette index of the sample in the row above is copied. In the‘INDEX’ mode, the palette index is explicitly signalled. For both‘INDEX’ and ‘COPY_ABOVE’ modes, a run value is signalled which specifiesthe number of subsequent samples that are also coded using the samemode. When escape symbol is part of the run in ‘INDEX’ or ‘COPY_ABOVE’mode, the escape component values are signalled for each escape symbol.The coding of palette indices is illustrated in FIG. 5 .

This syntax order is accomplished as follows. First the number of indexvalues for the CU is signaled. This is followed by signaling of theactual index values for the entire CU using truncated binary coding.Both the number of indices as well as the index values are coded inbypass mode. This groups the index-related bypass bins together. Thenthe palette sample mode (if necessary) and run are signaled in aninterleaved manner. Finally, the component escape values correspondingto the escape samples for the entire CU are grouped together and codedin bypass mode.

An additional syntax element, last_run_type_flag, is signaled aftersignaling the index values. This syntax element, in conjunction with thenumber of indices, eliminates the need to signal the run valuecorresponding to the last run in the block.

In HEVC-SCC, the palette mode is also enabled for 4:2:2, 4:2:0, andmonochrome chroma formats. The signaling of the palette entries andpalette indices is almost identical for all the chroma formats. In caseof non-monochrome formats, each palette entry consists of 3 components.For the monochrome format, each palette entry consists of a singlecomponent. For subsampled chroma directions, the chroma samples areassociated with luma sample indices that are divisible by 2. Afterreconstructing the palette indices for the CU, if a sample has only asingle component associated with it, only the first component of thepalette entry is used. The only difference in signaling is for theescape component values. For each escape sample, the number of escapecomponent values signaled may be different depending on the number ofcomponents associated with that sample.

In VVC, the dual tree coding structure is used on coding the intraslices, so the luma component and two chroma components may havedifferent palette and palette indices. In addition, the two chromacomponent shares same palette and palette indices.

FIG. 5 shows examples of coding of palette indices.

2.6 Intra Mode Coding in VVC

To capture the arbitrary edge directions presented in natural video, thenumber of directional intra modes in VTM5 is extended from 33, as usedin HEVC, to 65. The new directional modes not in HEVC are depicted asred dotted arrows in FIG. 6 and the planar and DC modes remain the same.These denser directional intra prediction modes apply for all blocksizes and for both luma and chroma intra predictions.

In VTM5, several conventional angular intra prediction modes areadaptively replaced with wide-angle intra prediction modes for thenon-square blocks.

In HEVC, every intra-coded block has a square shape and the length ofeach of its side is a power of 2. Thus, no division operations arerequired to generate an intra-predictor using DC mode. In VTM5, blockscan have a rectangular shape that necessitates the use of a divisionoperation per block in the general case. To avoid division operationsfor DC prediction, only the longer side is used to compute the averagefor non-square blocks.

FIG. 6 shows an example of 67 intra prediction modes.

To keep the complexity of the most probable mode (MPM) list generationlow, an intra mode coding method with 6 MPMs is used by considering twoavailable neighboring intra modes. The following three aspects areconsidered to construct the MPM list:

-   -   Default intra modes    -   Neighbouring intra modes    -   Derived intra modes

A unified 6-MPM list is used for intra blocks irrespective of whetherMRL and ISP coding tools are applied or not. The MPM list is constructedbased on intra modes of the left and above neighboring block. Supposethe mode of the left block is denoted as Left and the mode of the aboveblock is denoted as Above, the unified MPM list is constructed asfollows (The left and above blocks are shown in FIG. 7 ):

FIG. 7 is an example of the left and above neighbours of the currentblock.

-   -   When a neighboring block is not available, its intra mode is set        to Planar by default.    -   If both modes Left and Above are non-angular modes:        -   MPM list→{Planar, DC, V, H, V−4, V+4}    -   If one of modes Left and Above is angular mode, and the other is        non-angular:        -   Set a mode Max as the larger mode in Left and Above        -   MPM list→{Planar, Max, DC, Max−1, Max+1, Max−2}    -   If Left and Above are both angular and they are different:        -   Set a mode Max as the larger mode in Left and Above        -   if the difference of mode Left and Above is in the range of            2 to 62, inclusive    -   MPM list→{Planar, Left, Above, DC, Max−1, Max+1}        -   Otherwise    -   MPM list→{Planar, Left, Above, DC, Max−2, Max+2}    -   If Left and Above are both angular and they are the same:        -   MPM list→{Planar, Left, Left−1, Left+1, DC, Left−2}

Besides, the first bin of the mpm index codeword is CABAC context coded.In total three contexts are used, corresponding to whether the currentintra block is MRL enabled, ISP enabled, or a normal intra block.

During 6 MPM list generation process, pruning is used to removeduplicated modes so that only unique modes can be included into the MPMlist. For entropy coding of the 61 non-MPM modes, a Truncated BinaryCode (TBC) is used.

For chroma intra mode coding, a total of 8 intra modes are allowed forchroma intra mode coding. Those modes include five traditional intramodes and three cross-component linear model modes (CCLM, LM_A, andLM_L). Chroma mode signalling and derivation process are shown in Table2-. Chroma mode coding directly depends on the intra prediction mode ofthe corresponding luma block. Since separate block partitioningstructure for luma and chroma components is enabled in I slices, onechroma block may correspond to multiple luma blocks. Therefore, forChroma DM mode, the intra prediction mode of the corresponding lumablock covering the center position of the current chroma block isdirectly inherited.

TABLE 2-4 Derivation of chroma prediction mode from luma mode whencclm_is enabled Corresponding luma intra prediction mode X Chromaprediction mode 0 50 18 1 ( 0 <= X <= 66) 0 66 0 0 0 0 1 50 66 50 50 502 18 18 66 18 18 3 1 1 1 66 1 4 81 81 81 81 81 5 82 82 82 82 82 6 83 8383 83 83 7 0 50 18 1 X

2.7 Quantized Residual Block Differential Pulse-Code Modulation(QR-BDPCM)

In JVET-M0413, a quantized residual block differential pulse-codemodulation (QR-BDPCM) is proposed to code screen contents efficiently.

The prediction directions used in QR-BDPCM can be vertical andhorizontal prediction modes. The intra prediction is done on the entireblock by sample copying in prediction direction (horizontal or verticalprediction) similar to intra prediction. The residual is quantized andthe delta between the quantized residual and its predictor (horizontalor vertical) quantized value is coded. This can be described by thefollowing: For a block of size M (rows)×N (cols), let r_(i,j), 0≤i≤M−1,0≤j≤N−1 be the prediction residual after performing intra predictionhorizontally (copying left neighbor pixel value across the predictedblock line by line) or vertically (copying top neighbor line to eachline in the predicted block) using unfiltered samples from above or leftblock boundary samples. Let Q (r_(i,j)), 0≤i≤M−1, 0≤j≤N−1 denote thequantized version of the residual r_(i,j), where residual is differencebetween original block and the predicted block values. Then the blockDPCM is applied to the quantized residual samples, resulting in modifiedM×N array {tilde over (R)} with elements {tilde over (r)}_(i,j). Whenvertical BDPCM is signalled:

$\begin{matrix}{{\overset{\sim}{r}}_{i,j} = \left\{ \begin{matrix}{{Q\left( r_{i,j} \right)},} & {\ {{i = 0},\ {0 \leq j \leq \left( {N - 1} \right)}}} \\{{{{Q\left( r_{i,j} \right)} - {Q\left( r_{{({i - 1})},j} \right)}},}\ } & {{1 \leq i \leq \left( {M - 1} \right)}\ ,\ {0 \leq j \leq \left( {N - 1} \right)}}\end{matrix} \right.} & \left( {2\text{-}7\text{-}1} \right)\end{matrix}$

For horizontal prediction, similar rules apply, and the residualquantized samples are obtained by

$\begin{matrix}{{\overset{\sim}{r}}_{i,j} = \left\{ \begin{matrix}{{{Q\left( r_{i,j} \right)}\ ,}\ } & {{0 \leq i \leq \left( {M - 1} \right)},\ {j = 0}} \\{{{{Q\left( r_{i,j} \right)} - {Q\left( r_{i,{({j - 1})}} \right)}}\ ,}\ } & {{0 \leq i \leq \left( {M - 1} \right)}\ ,\ {1 \leq j \leq \left( {N - 1} \right)}}\end{matrix} \right.} & \left( {2\text{-}7\text{-}2} \right)\end{matrix}$

The residual quantized samples {tilde over (r)}_(i,j) are sent to thedecoder.

On the decoder side, the above calculations are reversed to produceQ(r_(i,j)), 0≤i≤M−1, 0≤j≤N−1. For vertical prediction case,

$\begin{matrix}{{{Q\left( r_{i,j} \right)} = {\sum\limits_{k = 0}^{i}{\overset{\sim}{r}}_{k,j}}},{0 \leq i \leq \left( {M - 1} \right)},{0 \leq j \leq \left( {N - 1} \right)}} & \left( {2\text{-}7\text{-}3} \right)\end{matrix}$

For horizontal case,

$\begin{matrix}{{{Q\left( r_{i,j} \right)} = {\sum\limits_{k = 0}^{j}{\overset{\sim}{r}}_{i,k}}},{0 \leq i \leq \left( {M - 1} \right)},{0 \leq j \leq \left( {N - 1} \right)}} & \left( {2\text{-}7\text{-}4} \right)\end{matrix}$

The inverse quantized residuals, Q⁻¹(Q(r_(i,j))), are added to the intrablock prediction values to produce the reconstructed sample values.

The main benefit of this scheme is that the inverse DPCM can be done onthe fly during coefficient parsing simply adding the predictor as thecoefficients are parsed or it can be performed after parsing.

2.8 Adaptive Loop Filter

In the VTM5, an Adaptive Loop Filter (ALF) with block-based filteradaption is applied. For the luma component, one among 25 filters isselected for each 4×4 block, based on the direction and activity oflocal gradients.

2.8.1.1 Filter Shape

In the VTM5, two diamond filter shapes (as shown in FIG. 8 ) are used.The 7×7 diamond shape is applied for luma component and the 5×5 diamondshape is applied for chroma components.

FIG. 8 shows examples of ALF filter shapes (chroma: 5×5 diamond, luma:7×7 diamond)

2.8.1.2 Block Classification

For luma component, each 4×4 block is categorized into one out of 25classes. The classification index Cis derived based on itsdirectionality D and a quantized value of activity Â, as follows:

$\begin{matrix}{C = {{5D} + \hat{A}}} & \left( {2\text{-}9\text{-}1} \right)\end{matrix}$

To calculate D and Â, gradients of the horizontal, vertical and twodiagonal direction are first calculated using 1-D Laplacian:

$\begin{matrix}{{g_{v} = {\sum\limits_{k = {i - 2}}^{i + 3}{\sum\limits_{l = {j - 2}}^{j + 3}V_{k,l,}}}},{V_{k,l} = {{{2{R\left( {k,l} \right)}} - {R\left( {k,{l - 1}} \right)} - {R\left( {k,{l + 1}} \right)}}}}} & \left( {2\text{-}9\text{-}2} \right) \\{{g_{h} = {\sum\limits_{k = {i - 2}}^{i + 3}{\sum\limits_{l = {j - 2}}^{j + 3}H_{k,l}}}},\ {H_{k,l} = {{{2{R\left( {k,l} \right)}} - {R\left( {{k - 1},l} \right)} - {R\left( {{k + 1},l} \right)}}}}} & \left( {2\text{-}1} \right) \\{{g_{d1} = {\sum\limits_{k = {i - 2}}^{i + 3}{\sum\limits_{l = {j - 3}}^{j + 3}{D1}_{k,l}}}},{{D\; 1_{k,l}} = \left| {{2{R\left( {k,l} \right)}} - {R\left( {{k - 1},{l - 1}} \right)} - {R\left( {{k + 1},{l + 1}} \right)}} \right|}} & \left( {2\text{-}9\text{-}4} \right) \\{{g_{d2} = {\sum\limits_{k = {i - 2}}^{i + 3}{\sum\limits_{l = {j - 2}}^{j + 3}{D2}_{k,l}}}},{{D\; 2_{k,l}} = {{{2{R\left( {k,l} \right)}} - {R\left( {{k - 1},{l + 1}} \right)} - {R\left( {{k + 1},{l - 1}} \right)}}}}} & \left( {2\text{-}9\text{-}5} \right)\end{matrix}$

Where indices i and j refer to the coordinates of the upper left samplewithin the 4×4 block and R(i,j) indicates a reconstructed sample atcoordinate (i,j).

To reduce the complexity of block classification, the subsampled 1-DLaplacian calculation is applied. As shown in FIG. 9 the same subsampledpositions are used for gradient calculation of all directions.

FIG. 9 shows an example of subsampled Laplacian calculation. (a)Subsampled positions for vertical gradient (b) Sub sampled positions forhorizontal gradient (c) Sub sampled positions for diagonal gradient (d)Subsampled positions for diagonal gradient.

Then D maximum and minimum values of the gradients of horizontal andvertical directions are set as:

$\begin{matrix}{{g_{h,v}^{\max} = {\max\left( {g_{h},g_{v}} \right)}},{g_{h,v}^{\min} = {\min\left( {g_{h},g_{v}} \right)}}} & \left( {2\text{-}9\text{-}6} \right)\end{matrix}$

The maximum and minimum values of the gradient of two diagonaldirections are set as:

$\begin{matrix}{{g_{{d\; 0},{d\; 1}}^{\max} = {\max\left( {g_{d\; 0},g_{d1}} \right)}},{g_{{d\; 0},{d\; 1}}^{\min} = {\min\left( {g_{d\; 0},g_{d1}} \right)}}} & \left( {2\text{-}9\text{-}7} \right)\end{matrix}$

To derive the value of the directionality D, these values are comparedagainst each other and with two thresholds t₁ and t₂:

Step 1. If both g_(h,v) ^(max)≤t₁·g_(h,v) ^(min) and g_(d0,d1)^(max)≤t₁·g_(d0,d1) ^(min) are true, D is set to 0.

Step 2. If g_(h,v) ^(max)/g_(h,v) ^(min)>g_(d0,d1) ^(max)/g_(d0,d1)^(min), continue from Step 3; otherwise continue from Step 4.

Step 3. If g_(h,v) ^(max)>t₂·g_(h,v) ^(min), D is set to 2; otherwise Dis set to 1.

Step 4. If g_(d0,d1) ^(max)>t₂·g_(d0,d1) ^(min), D is set to 4;otherwise D is set to 3.

The activity value A is calculated as:

$\begin{matrix}{A = {\sum\limits_{k = {i - 2}}^{i + 3}{\sum\limits_{l = {j - 2}}^{j + 3}\left( {V_{k,l} + H_{k,l}} \right)}}} & \left( {2\text{-}9\text{-}8} \right)\end{matrix}$

A is further quantized to the range of 0 to 4, inclusively, and thequantized value is denoted as Â.

For chroma components in a picture, no classification method is applied,i.e. a single set of ALF coefficients is applied for each chromacomponent.

2.8.1.3 Geometric Transformations of Filter Coefficients and ClippingValues

Before filtering each 4×4 luma block, geometric transformations such asrotation or diagonal and vertical flipping are applied to the filtercoefficients f(k,l) and to the corresponding filter clipping valuesc(k,l) depending on gradient values calculated for that block. This isequivalent to applying these transformations to the samples in thefilter support region. The idea is to make different blocks to which ALFis applied more similar by aligning their directionality.

Three geometric transformations, including diagonal, vertical flip androtation are introduced:

$\begin{matrix}{\mspace{20mu}{{{{Diagonal}\text{:}\mspace{14mu}{f_{D}\left( {k,l} \right)}} = {f\left( {l,k} \right)}},{{c_{D}\left( {k,l} \right)} = {c\left( {l,k} \right)}},}} & \left( {2\text{-}9\text{-}9} \right) \\{{{{Vertical}\mspace{14mu}{flip}\text{:}\mspace{14mu}{f_{V}\left( {k,l} \right)}} = {f\left( {k,{K - l - 1}} \right)}},{{c_{V}\left( {k,l} \right)} = {c\left( {k,{K - l - 1}} \right)}}} & \left( {2\text{-}9\text{-}10} \right) \\{{{{Rotation}\text{:}\mspace{14mu}{f_{R}\left( {k,l} \right)}} = {f\left( {{K - l - 1},k} \right)}},{{c_{R}\left( {k,l} \right)} = {c\left( {{K - l - 1},k} \right)}}} & \left( {2\text{-}9\text{-}11} \right)\end{matrix}$

where K is the size of the filter and 0≤k,l≤K−1 are coefficientscoordinates, such that location (0,0) is at the upper left corner andlocation (K−1, K−1) is at the lower right corner. The transformationsare applied to the filter coefficients f(k,l) and to the clipping valuesc(k,l) depending on gradient values calculated for that block. Therelationship between the transformation and the four gradients of thefour directions are summarized in the following table.

TABLE 2-5 Mapping of the gradient calculated for one block and thetransformations Gradient values Transformation g_(d2) < g_(d1) and g_(h)< g_(v) No transformation g_(d2) < g_(d1) and g_(v) < g_(h) Diagonalg_(d1) < g_(d2) and g_(h) < g_(v) Vertical flip g_(d1) < g_(d2) andg_(v) < g_(h) Rotation

2.8.1.4 Filter Parameters Signalling

In the VTM5, ALF filter parameters are signalled in Adaptation ParameterSet (APS). In one APS, up to 25 sets of luma filter coefficients andclipping value indexes, and up to one set of chroma filter coefficientsnd clipping value indexes could be signalled. To reduce bits overhead,filter coefficients of different classification can be merged. In sliceheader, the indices of the APSs used for the current slice are signaled.

Clipping value indexes, which are decoded from the APS, allowdetermining clipping values using a Luma table of clipping values and aChroma table of clipping values. These clipping values are dependent ofthe internal bitdepth. More precisely, the Luma table of clipping valuesand Chroma table of clipping values are obtained by the followingformulas:

$\begin{matrix}{{AlfClip}_{L}{\left\{ {{{round}\mspace{14mu}\left( 2^{B\frac{N - n + 1}{N}} \right)\mspace{14mu}{for}\mspace{14mu} n} \in \left\lbrack {1\mspace{14mu}\ldots\mspace{14mu} N} \right\rbrack} \right\}.}} & \left( {2\text{-}9\text{-}10} \right) \\{{AlfClip}_{C} = \left\{ {{{round}\mspace{14mu}\left( {2^{{({B - 8})} + 8}\frac{\left( {N - n} \right)}{N - 1}} \right)\mspace{14mu}{for}\mspace{14mu} n} \in \left\lbrack {1\mspace{20mu}\ldots\mspace{14mu} N} \right\rbrack} \right\}} & \left( {2\text{-}9\text{-}13} \right)\end{matrix}$

with B equal to the internal bitdepth and N equal to 4 which is thenumber of allowed clipping values in VTM5.0.

The filtering process can be controlled at CTB level. A flag is alwayssignalled to indicate whether ALF is applied to a luma CTB. A luma CTBcan choose a filter set among 16 fixed filter sets and the filter setsfrom APSs. A filter set index is signaled for a luma CTB to indicatewhich filter set is applied. The 16 fixed filter sets are pre-definedand hard-coded in both the encoder and the decoder.

The filter coefficients are quantized with norm equal to 128. In orderto restrict the multiplication complexity, a bitstream conformance isapplied so that the coefficient value of the non-central position shallbe in the range of −2⁷ to 2⁷−1, inclusive. The central positioncoefficient is not signalled in the bitstream and is considered as equalto 128.

2.8.1.5 Filtering Process

At decoder side, when ALF is enabled for a CTB, each sample R(i,j)within the CU is filtered, resulting in sample value R′(i,j) as shownbelow,

$\begin{matrix}{{R^{\prime}\left( {i,j} \right)} = {{R\left( {i,j} \right)} + \left( {\left( {{\sum\limits_{k \neq 0}{\sum\limits_{l \neq 0}{{f\left( {k,l} \right)} \times {K\left( {{{R\left( {{i + k},{j + l}} \right)} - {R\left( {i,j} \right)}},\ {c\left( {k,l} \right)}} \right)}}}} + 64} \right)\operatorname{>>}7} \right)}} & \left( {2\text{-}9\text{-}14} \right)\end{matrix}$

where f(k,l) denotes the decoded filter coefficients, K(x,y) is theclipping function and c(k,l) denotes the decoded clipping parameters.The variable k and l varies between

${- \frac{L}{2}}\mspace{14mu}{and}\mspace{14mu}\frac{L}{2}$where L denotes the filter length. The clipping function K(x,y)=min (y,max(−y,x)) which corresponds to the function Clip3 (−y,y,x).

2.8.1.6 Virtual Boundary Filtering Process for Line Buffer Reduction

In VTM5, to reduce the line buffer requirement of ALF, modified blockclassification and filtering are employed for the samples nearhorizontal CTU boundaries. For this purpose, a virtual boundary isdefined as a line by shifting the horizontal CTU boundary with “N”samples as shown in FIG. 10 with N equal to 4 for the Luma component and2 for the Chroma component

FIG. 10 shows an example of a modified block classification at virtualboundaries.

Modified block classification is applied for the Luma component asdepicted in FIG. 11 activity value A is accordingly scaled by takinginto account the reduced number of samples used in 1D Laplacian gradientcalculation.

For filtering processing, symmetric padding operation at the virtualboundaries are used for both Luma and Chroma components. As shown inFIG. 11 , when the sample being filtered is located below the virtualboundary, the neighboring samples that are located above the virtualboundary are padded. Meanwhile, the corresponding samples at the othersides are also padded, symmetrically.

FIG. 11 shows examples of modified ALF filtering for Luma component atvirtual boundaries.

2.9 Sample Adaptive Offset (SAO)

Sample adaptive offset (SAO) is applied to the reconstructed signalafter the deblocking filter by using offsets specified for each CTB bythe encoder. The HM encoder first makes the decision on whether or notthe SAO process is to be applied for current slice. If SAO is appliedfor the slice, each CTB is classified as one of five SAO types as shownin Table 2-. The concept of SAO is to classify pixels into categoriesand reduces the distortion by adding an offset to pixels of eachcategory. SAO operation includes Edge Offset (EO) which uses edgeproperties for pixel classification in SAO type 1-4 and Band Offset (BO)which uses pixel intensity for pixel classification in SAO type 5. Eachapplicable CTB has SAO parameters including sao_merge_left_flag,sao_merge_up_flag, SAO type and four offsets. If sao_merge_left flag isequal to 1, the current CTB will reuse the SAO type and offsets of theCTB to the left. If sao_merge_up_flag is equal to 1, the current CTBwill reuse SAO type and offsets of the CTB above.

TABLE 2-6 Specification of SAO type sample adaptive offset type toNumber of SAO type be used categories 0 None 0 1 1-D 0-degree patternedge offset 4 2 1-D 90-degree pattern edge offset 4 3 1-D 135-degreepattern edge 4 offset 4 1-D 45-degree pattern edge offset 4 5 bandoffset 4

2.9.1 Operation of Each SAO Type

Edge offset uses four 1-D 3-pixel patterns for classification of thecurrent pixel p by consideration of edge directional information, asshown in FIG. 12 . From left to right these are: 0-degree, 90-degree,135-degree and 45-degree.

FIG. 12 shows examples of four 1-D 3-pixel patterns for the pixelclassification in EO.

Each CTB is classified into one of five categories according to Table2-7.

TABLE 2-7 Pixel classification rule for EO Category Condition Meaning 0None of the below Largely monotonic 1 p < 2 neighbours Local minimum 2 p< 1 neighbour && p = = 1 Edge neighbour 3 p > 1 neighbour && p = = 1Edge neighbour 4 p > 2 neighbours Local maximum

Band offset (BO) classifies all pixels in one CTB region into 32 uniformbands by using the five most significant bits of the pixel value as theband index. In other words, the pixel intensity range is divided into 32equal segments from zero to the maximum intensity value (e.g. 255 for8-bit pixels). Four adjacent bands are grouped together and each groupis indicated by its most left-hand position as shown in FIG. 13 . Theencoder searches all position to get the group with the maximumdistortion reduction by compensating offset of each band.

FIG. 13 shows an example of four bands are grouped together andrepresented by its starting band position

2.10 Combined Inter and Intra Prediction (CHIP)

In VTM5, when a CU is coded in merge mode, if the CU contains at least64 luma samples (that is, CU width times CU height is equal to or largerthan 64), and if both CU width and CU height are less than 128 lumasamples, an additional flag is signalled to indicate if the combinedinter/intra prediction (CIIP) mode is applied to the current CU. As itsname indicates, the CIIP prediction combines an inter prediction signalwith an intra prediction signal. The inter prediction signal in the CIIPmode P_(inter) is derived using the same inter prediction processapplied to regular merge mode; and the intra prediction signal P_(intra)is derived following the regular intra prediction process with theplanar mode. Then, the intra and inter prediction signals are combinedusing weighted averaging, where the weight value is calculated dependingon the coding modes of the top and left neighbouring blocks (depicted inFIG. 14 ) as follows:

-   -   If the top neighbor is available and intra coded, then set        isIntraTop to 1, otherwise set isIntraTop to 0;    -   If the left neighbor is available and intra coded, then set        isIntraLeft to 1, otherwise set isIntraLeft to 0;    -   If (isIntraLeft+isIntraLeft) is equal to 2, then wt is set to 3;    -   Otherwise, if (isIntraLeft+isIntraLeft) is equal to 1, then wt        is set to 2;    -   Otherwise, set wt to 1.

The CIIP prediction is formed as follows:

$\begin{matrix}{{P_{CIIP} = \left( {{\left( {4 - {wt}} \right)*P_{inter}} + {{wt}*P_{intra}} + 2} \right)}\operatorname{>>}2} & \left( {3\text{-}2} \right)\end{matrix}$

FIG. 14 shows examples of Top and left neighboring blocks used in CIIPweight derivation

2.11 Luma Mapping with Chroma Scaling (LMCS)

In VTM5, a coding tool called the luma mapping with chroma scaling(LMCS) is added as a new processing block before the loop filters. LMCShas two main components: 1) in-loop mapping of the luma component basedon adaptive piecewise linear models; 2) for the chroma components,luma-dependent chroma residual scaling is applied. FIG. 15 shows theLMCS architecture from decoder's perspective. In the blocks of FIG. 15 ,which include the inverse quantization, inverse transform, luma intraprediction and adding of the luma prediction together with the lumaresidual, the processing is applied in the mapped domain. The unshadedblocks in FIG. 15 indicate where the processing is applied in theoriginal (i.e., non-mapped) domain; and these include loop filters suchas deblocking, ALF, and SAO, motion compensated prediction, chroma intraprediction, adding of the chroma prediction together with the chromaresidual, and storage of decoded pictures as reference pictures. FIG. 15show the new LMCS functional blocks that include forward and inversemapping of the luma signal and a luma-dependent chroma scaling process.Like most other tools in VVC, LMCS can be enabled/disabled at thesequence level using an SPS flag.

FIG. 15 shows examples of Luma mapping with chroma scaling architecture.

2.12 Dualtree Partitioning

In the current VVC design, for I slices, each CTU can be split intocoding units with 64×64 luma samples using an implicit quadtree splitand that these coding units are the root of two separate coding_treesyntax structure for luma and chroma.

Since the dual tree in intra picture allows to apply differentpartitioning in the chroma coding tree compared to the luma coding tree,the dual tree introduces longer coding pipeline and the QTBT MinQTSizeCvalue range and MinBtSizeY and MinTTSizeY in chroma tree allow smallchroma blocks such as 2×2, 4×2, and 2×4. It provides difficulties inpractical decoder design. Moreover, several prediction modes such asCCLM, planar and angular mode needs multiplication. In order toalleviate the above-mentioned issues, small chroma block sizes(2×2/2×4/4×2) are restricted in dual tree as a partitioning restriction.

2.13 Smallest Chroma Intra Prediction Unit (SCIPU) in JVET-O0050

Small chroma size is not friendly to hardware implementation. Indualtree cases, chroma blocks with too small sizes are disallowed.However, in singletree cases, VVC draft 5 still allows 2×2, 2×4, 4×2chroma blocks. To restrict the size of chroma block, in single codingtree, a SCIPU is defined in JVET-O0050 as a coding tree node whosechroma block size is larger than or equal to TH chroma samples and hasat least one child luma block smaller than 4TH luma samples, where TH isset to 16 in this contribution. It is required that in each SCIPU, allCBs are inter, or all CBs are non-inter, i.e, either intra or IBC. Incase of a non-inter SCIPU, it is further required that chroma of thenon-inter SCIPU shall not be further split and luma of the SCIPU isallowed to be further split. In this way, the smallest chroma intra CBsize is 16 chroma samples, and 2×2, 2×4, and 4×2 chroma CBs are removed.In addition, chroma scaling is not applied in case of a non-inter SCIPU.

Two SCIPU examples are shown in FIG. 16 . In FIG. 16(a), one chroma CBof 8×4 chroma samples and three luma CBs (4×8, 8×8, 4×8 luma CBs) formone SCIPU because the ternary tree (TT) split from the 8×4 chromasamples would result in chroma CBs smaller than 16 chroma samples. InFIG. 16(b), one chroma CB of 4×4 chroma samples (the left side of the8×4 chroma samples) and three luma CBs (8×4, 4×4, 4×4 luma CBs) form oneSCIPU, and the other one chroma CB of 4×4 samples (the right side of the8×4 chroma samples) and two luma CBs (8×4, 8×4 luma CBs) form one SCIPUbecause the binary tree (BT) split from the 4×4 chroma samples wouldresult in chroma CBs smaller than 16 chroma samples.

FIG. 16 shows SCIPU examples.

The type of a SCIPU is inferred to be non-inter if the current slice isan I-slice or the current SCIPU has a 4×4 luma partition in it afterfurther split one time (because no inter 4×4 is allowed in VVC);otherwise, the type of the SCIPU (inter or non-inter) is indicated byone signalled flag before parsing the CUs in the SCIPU.

2.14 Small Chroma Block Constrains in VVC Draft 6

In VVC draft 6 (JVET-O2001-vE.docx), the constrains on small chromablocks are implemented as follows (related part is marked in

).

coding tree( x0, y0, cbWidth, cbHeight, qgOnY, qgOnC, cb Subdiv,cqtDepth, mttDepth, depthOffset, partIdx,

 

 { Descriptor . . . if( split_cu_flag ) { if( ( allowSplitBtVer | |allowSplitBtHor | | allowSplitTtVer | | allowSplitTtHor) && allowSplitQT) split_qt_flag ae(v) if( !split_qt_flag ) { if( ( allowSplitBtHor | |allowSplitTtHor ) && ( allowSplitBtVer | | allowSplitTtVer ) )mtt_split_cu_vertical_flag ae(v) if( ( allowSplitBtVer &&allowSplitTtVer && mtt_split_cu_vertical_flag) | | ( allowSplitBtHor &&allowSplitTtHor && !mtt_split_cu_vertical_flag ) )mtt_split_cu_binary_flag ae(v) }

ae(v)

 

= =

if( !split_qt_flag ) { if( MttSplitMode[ x0 ][ y0 ][ mttDepth ] = =SPLIT_BT_VER) { depthOffset += ( x0 +cbWidth > pic_width_in_luma_samples) ? 1 : 0 x1 = x0 + ( cbWidth / 2 ) coding_tree( x0, y0, cbWidth/ 2,cbHeight, qgOnY, qgOnC, cbSubdiv + 1, cqtDepth, mttDepth + 1,depthOffset, 0, treeType, modeType) if( x1 <pic_width_in_luma_samples)coding_tree( x1, y0, cbWidth / 2, cbHeightY, qgOnY, qgOnC, cbSubdiv + 1,cqtDepth, mttDepth + 1, depthOffset, 1, treeType, modeType) } else if(MttSplitMode[ x0 ][ y0 ][ mttDepth ] = = SPLIT_BT_HOR ) { depthOffset +=(y0 + cbHeight > pic_height_in_luma_samples ) ? 1 : 0 y1 = y0 +(cbHeight / 2 ) coding_tree( x0, y0, cbWidth, cbHeight / 2, qgOnY, qgOnC,cbSubdiv + 1, cqtDepth, mttDepth + 1, depthOffset, 0, treeType,modeType) if( y1 < pic_height_in_luma_samples) coding tree( x0, y1,cbWidth, cbHeight / 2, qgOnY, qgOnC, cbSubdiv + 1, cqtDepth, mttDepth +1, depthOffset, 1, treeType, modeType) } else if( MttSplitMode[ x0 ][ y0][ mttDepth] = = SPLIT_TT_VER) { x1 = x0 + ( cbWidth / 4 ) x2 = x0 + (3 * cbWidth / 4 ) qgOnY = qgOnY && ( cbSubdiv + 2 <= cu_qp_delta_subdiv) qgOnC = qgOnC && ( cbSubdiv + 2 <= cu_chroma_qp_offset_subdiv ) codingtree( x0, y0, cbWidth/ 4, cbHeight, qgOnY, qgOnC, cbSubdiv + 2,cqtDepth, mttDepth + 1, depthOffset, 0, treeType, modeType) coding tree(xl, y0, cbWidth/ 2, cbHeight, qgOnY, qgOnC, cbSubdiv + 1, cqtDepth,mttDepth + 1, depthOffset, 1, treeType, modeType) coding tree( x2, y0,cbWidth/ 4, cbHeight, qgOnY, qgOnC, cbSubdiv + 2, cqtDepth, mttDepth +1, depthOffset, 2, treeType, modeType) } else {/* SPLIT_TT_HOR */ y1 =y0 + ( cbHeight / 4 ) y2 = y0 + ( 3 * cbHeight / 4 ) qgOnY = qgOnY && (cbSubdiv + 2 <= cu_qp_delta_subdiv ) qgOnC = qgOnC && ( cb Sub div + 2<= cu_chroma_qp_offset_subdiv ) coding_tree( x0, y0, cbWidth, cbHeight /4, qgOnY, qgOnC, cbSubdiv + 2, cqtDepth, mttDepth + 1, depthOffset, 0,treeType, modeType) coding tree( x0, y1, cbWidth, cbHeight / 2, qgOnY,qgOnC, cbSubdiv + 1, cqtDepth, mttDepth + 1, depthOffset, 1, treeType,modeType) coding tree( x0, y2, cbWidth, cbHeight / 4, qgOnY, qgOnC,cbSubdiv + 2, cqtDepth, mttDepth + 1, depthOffset, 2, treeType,modeType) } } else { x1 = x0 + ( cbWidth / 2 ) y1 = y0 + ( cbHeight / 2) coding_tree( x0, y0, cbWidth/ 2, cbHeight / 2, qgOnY, qgOnC,cbSubdiv + 2, cqtDepth + 1, 0, 0, 0, treeType, modeType ) if( x1<pic_width_in_luma_samples) coding_tree( x1, y0, cbWidth/ 2, cbHeight/2, qgOnY, qgOnC, cbSubdiv + 2, cqtDepth + 1, 0, 0, 1, treeType, modeType) if( y1 < pic_height_in_luma_samples ) coding_tree( x0, y1, cbWidth/ 2,cbHeight/ 2, qgOnY, qgOnC, cbSubdiv + 2, cqtDepth + 1, 0, 0, 2,treeType, modeType ) if( y1 < pic_height_in_luma_samples && x1 <pic_width_in_luma_samples) coding_tree( x1, y1, cbWidth/ 2, cbHeight/ 2,qgOnY, qgOnC, cb Subdiv + 2, cqtDepth + 1, 0, 0, 3, treeType, modeType )}

 

  } else coding_unit( x0, y0, cbWidth, cbHeight, cqtDepth, treeTypeCurr,modeTypeCurr ) }

-   -   -   

    -   -   

        -   

        -   

    -   -   

        -   

    -   

Allowed Quad Split Process

Inputs to this process are:

-   -   a coding block size cb Size in luma samples,    -   a multi-type tree depth mttDepth,    -   a variable treeType specifying whether a single tree        (SINGLE_TREE) or a dual tree is used to partition the CTUs and,        when a dual tree is used, whether the luma (DUAL_TREE_LUMA) or        chroma components (DUAL_TREE_CHROMA) are currently processed,    -   inter coding modes can be used (MODE_TYPE_INTER) for coding        units inside the coding tree node.        Output of this process is the variable allowSplitQt.        The variable allowSplitQt is derived as follows:    -   If one or more of the following conditions are true,        allowSplitQt is set equal to FALSE:        -   treeType is equal to SINGLE_TREE or DUAL_TREE_LUMA and            cbSize is less than or equal to MinQtSizeY        -   treeType is equal to DUAL_TREE_CHROMA and cbSize/SubWidthC            is less than or equal to MinQtSizeC        -   mttDepth is not equal to 0        -   treeType is equal to DUAL_TREE_CHROMA and (cbSize/SubWidthC)            is less than or equal to 4        -   treeType is equal to DUAL_TREE_CHROMA and modeType is equal            to MODE_TYPE_INTRA    -   Otherwise, allowSplitQt is set equal to TRUE.        Allowed Binary Split Process        Inputs to this process are:    -   a binary split mode btSplit,    -   a coding block width cbWidth in luma samples,    -   a coding block height cbHeight in luma samples,    -   a location (x0, y0) of the top-left luma sample of the        considered coding block relative to the top-left luma sample of        the picture,    -   a multi-type tree depth mttDepth,    -   a maximum multi-type tree depth with offset maxMttDepth,    -   a maximum binary tree size maxBtSize,    -   a minimium quadtree size minQtSize,    -   a partition index partIdx,    -   a variable treeType specifying whether a single tree        (SINGLE_TREE) or a dual tree is used to partition the CTUs and,        when a dual tree is used, whether the luma (DUAL_TREE_LUMA) or        chroma components (DUAL_TREE_CHROMA) are currently processed,    -           Output of this process is the variable allowBtSplit.

TABLE 6-2 Specification of parallelTtSplit and cbSize based on btSplit.btSplit = = btSplit = = SPLIT_BT_VER SPLIT_BT_HOR parallelTtSplitSPLIT_TT_VER SPLIT_TT_HOR cbSize cbWidth cbHeightThe variables parallelTtSplit and cbSize are derived as specified inTable 6-2.The variable allowBtSplit is derived as follows:

-   -   If one or more of the following conditions are true,        allowBtSplit is set equal to FALSE:        -   cb Size is less than or equal to MinBtSizeY        -   cbWidth is greater than maxBtSize        -   cbHeight is greater than maxBtSize        -   mttDepth is greater than or equal to maxMttDepth        -   treeType is equal to DUAL_TREE_CHROMA and            (cbWidth/SubWidthC)*(cbHeight/SubHeightC) is less than or            equal to 16

    -   

    -   Otherwise, if all of the following conditions are true,        allowBtSplit is set equal to FALSE        -   btSplit is equal to SPLIT_BT_VER        -   y0+cbHeight is greater than pic_height_in_luma_samples

    -   Otherwise, if all of the following conditions are true,        allowBtSplit is set equal to FALSE        -   btSplit is equal to SPLIT_BT_VER        -   cbHeight is greater than MaxTbSizeY        -   x0+cbWidth is greater than pic_width_in_luma_samples

    -   Otherwise, if all of the following conditions are true,        allowBtSplit is set equal to FALSE        -   btSplit is equal to SPLIT_BT_HOR        -   cbWidth is greater than MaxTbSizeY        -   y0+cbHeight is greater than pic_height_in_luma_samples

    -   Otherwise, if all of the following conditions are true,        allowBtSplit is set equal to FALSE        -   x0+cbWidth is greater than pic_width_in_luma_samples        -   y0+cbHeight is greater than pic_height_in_luma_samples        -   cbWidth is greater than minQtSize

    -   Otherwise, if all of the following conditions are true,        allowBtSplit is set equal to FALSE        -   btSplit is equal to SPLIT_BT_HOR        -   x0+cbWidth is greater than pic_width_in_luma_samples        -   y0+cbHeight is less than or equal to            pic_height_in_luma_samples

    -   Otherwise, if all of the following conditions are true,        allowBtSplit is set equal to FALSE:        -   mttDepth is greater than 0        -   partIdx is equal to 1        -   MttSplitMode[x0][y0][mttDepth−1] is equal to parallelTtSplit

    -   Otherwise, if all of the following conditions are true,        allowBtSplit is set equal to FALSE        -   btSplit is equal to SPLIT_BT_VER        -   cbWidth is less than or equal to MaxTbSizeY        -   cbHeight is greater than MaxTbSizeY

    -   Otherwise, if all of the following conditions are true,        allowBtSplit is set equal to FALSE        -   btSplit is equal to SPLIT_BT_HOR        -   cbWidth is greater than MaxTbSizeY        -   cbHeight is less than or equal to MaxTbSizeY

    -   Otherwise, allowBtSplit is set equal to TRUE.        Allowed Ternary Split Process        Inputs to this process are:

    -   a ternary split mode ttSplit,

    -   a coding block width cbWidth in luma samples,

    -   a coding block height cbHeight in luma samples,

    -   a location (x0, y0) of the top-left luma sample of the        considered coding block relative to the top-left luma sample of        the picture,

    -   a multi-type tree depth mttDepth

    -   a maximum multi-type tree depth with offset maxMttDepth,

    -   a maximum ternary tree size maxTtSize,

    -   a variable treeType specifying whether a single tree        (SINGLE_TREE) or a dual tree is used to partition the CTUs and,        when a dual tree is used, whether the luma (DUAL_TREE_LUMA) or        chroma components (DUAL_TREE_CHROMA) are currently processed,

    -           Output of this process is the variable allowTtSplit.

TABLE 6-3 Specification of cbSize based on ttSplit. ttSplit = =SPLIT_TT_VER ttSplit = = SPLIT_TT_HOR cbSize cbWidth cbHeightThe variable cbSize is derived as specified in Table 6-3.The variable allowTtSplit is derived as follows:

-   -   If one or more of the following conditions are true,        allowTtSplit is set equal to FALSE:        -   cb Size is less than or equal to 2*MinTtSizeY

        -   cbWidth is greater than Min(MaxTbSizeY, maxTtSize)

        -   cbHeight is greater than Min(MaxTbSizeY, maxTtSize)

        -   mttDepth is greater than or equal to maxMttDepth

        -   x0+cbWidth is greater than pic_width_in_luma_samples

        -   y0+cbHeight is greater than pic_height_in_luma_samples

        -   treeType is equal to DUAL_TREE_CHROMA and            (cbWidth/SubWidthC)*(cbHeight/SubHeightC) is less than or            equal to 32

        -   

    -   Otherwise, allowTtSplit is set equal to TRUE.        pred_mode_flag equal to 0 specifies that the current coding unit        is coded in inter prediction mode.        pred_mode_flag equal to 1 specifies that the current coding unit        is coded in intra prediction mode.        When pred_mode_flag is not present, it is inferred as follows:

    -   If cbWidth is equal to 4 and cbHeight is equal to 4,        pred_mode_flag is inferred to be equal to 1.

    -   

    -   

    -   Otherwise, pred_mode_flag is inferred to be equal to 1 when        decoding an I slice, and equal to 0 when decoding a P or B        slice, respectively.        The variable CuPredMode[chType][x][y] is derived as follows for        x=x0 . . . x0+cbWidth−1 and y=y0 . . . y0+cbHeight−1:

    -   If pred_mode_flag is equal to 0, CuPredMode[chType][x][y] is set        equal to MODE_INTER.

    -   Otherwise (pred_mode_flag is equal to 1),        CuPredMode[chType][x][y] is set equal to MODE_INTRA.        pred_mode_ibc_flag equal to 1 specifies that the current coding        unit is coded in IBC prediction mode. pred_mode_ibc_flag equal        to 0 specifies that the current coding unit is not coded in IBC        prediction mode.        When pred_mode_ibc_flag is not present, it is inferred as        follows:

    -   If cu_skip_flag[x0][y0] is equal to 1, and cbWidth is equal to        4, and cbHeight is equal to 4, pred_mode_ibc_flag is inferred to        be equal 1.

    -   Otherwise, if both cbWidth and cbHeight are equal to 128,        pred_mode_ibc_flag is inferred to be equal to 0.

    -   

    -   

    -   Otherwise, pred_mode_ibc_flag is inferred to be equal to the        value of sps_ibc_enabled_flag when decoding an I slice, and 0        when decoding a P or B slice, respectively.        When pred_mode_ibc_flag is equal to 1, the variable        CuPredMode[chType][x][y] is set to be equal to MODE_IBC for x=x0        . . . x0+cbWidth−1 and y=y0 . . . y0+cbHeight−1.

3. Problems

-   -   1. Currently IBC is considered as MODE_TYPE_INTRA and thus small        chroma block is disallowed, which leads to unnecessary coding        efficiency loss.    -   2. Currently palette is considered as MODE_TYPE_INTRA and thus        small chroma block is disallowed, which leads to unnecessary        coding efficiency loss.    -   3. Currently small chroma block constrains do not consider color        subsampling format.    -   4. Currently same partition and prediction mode constraints on        small blocks is applied to all chroma formats. However, it may        be desirable to design different constraint mechanisms on small        blocks in 4:2:0 and 4:2:2 chroma formats.    -   5. Currently the Palette mode flag signaling depends on the        modeType, which is not desirable as palette may be not apply        small block constraints.    -   6. Currently the IBC mode flag is inferred to be 0 for P/B slice        with cu_skip_flag equal to 1 but MODE_TYPE equal to        MODE_TYPE_INTRA, this is illegal in the syntax parsing.    -   7. Currently, non-4×4 luma IBC mode is not allowed for SCIPU        luma blocks, which may be not desirable and may cause coding        efficiency loss.    -   8. 2×H chroma block is still allowed, which is not friendly to        hardware implementation.    -   9. CIIP is considered as of MODE_INTER while it uses intra        prediction, which breaks the constrains in some cases.

4. Examples of Technical Solutions and Embodiments

The listing below should be considered as examples. These techniquesshould not be interpreted in a narrow way. Furthermore, these techniquescan be combined in any manner.

In this document, “M×N coding tree node” indicates a M×N block, with Mas the block width and N as the block height in luma samples, which maybe further partitioned, such as by QT/BT/TT. For example, a block couldbe a QT node, or a BT node, or a TT node. A coding tree node could be acoding unit (e.g., with three color components for single tree, with twochroma color components for dual tree chroma coding, and only luma colorcomponent for dual tree luma coding), or a luma coding block, or achroma coding block. A “small coding tree node unit” may indicate acoding tree node with block size M×N equal to 32/64/128 in luma samples.

If not specifically mentioned, the width W and height H for a codingblock is measured in luma samples. For example, M×N coding block means aM×N luma block, and/or two (M/SubWidthC)×(N/SubHeightC) chroma blocks,where SubWidthC and SubHeightC are derived by chroma format as below.

chroma_ separate_colour_ Chroma SubWidth SubHeight format_idc plane_flagformat C C 0 0 Monochrome 1 1 1 0 4:2:0 2 2 2 0 4:2:2 2 1 3 0 4:4:4 1 13 1 4:4:4 1 1

-   1. Whether and/or how to partition into small blocks may depend on    color formats.    -   a. In one example, for 4:4:4 color format, the constrains on the        sizes of chroma blocks may follow those constrains on luma        blocks.    -   b. In one example, for 4:2:2 color format, the constrains on the        sizes of chroma blocks may follow those constrains for 4:2:0        color format.    -   c. In one example, for 4:0:0, and/or 4:4:4 chroma format, the        constraints on small block partitions and/or prediction modes        may be not applied.    -   d. In one example, the constraints on small block partitions        and/or prediction modes may be applied differently for different        chroma formats.        -   i. In one example, for M×N (such as 8×8) coding tree node            with horizontal BT split, in 4:2:2 chroma format, the            horizontal BT split may be allowed for both chroma block and            luma block, while in 4:2:0 chroma format, the horizontal BT            split may be allowed for luma block but disabled for chroma            block.        -   ii. In one example, for M×N (such as 16×4) coding tree node            with vertical BT split, in 4:2:2 chroma format, the vertical            BT split may be allowed for both chroma block and luma            block, while in 4:2:0 chroma format, the vertical BT split            may be allowed for luma block but disabled for chroma block.        -   iii. In one example, for M×N (such as 8×16) coding tree node            with horizontal TT split, in 4:2:2 chroma format, the            horizontal TT split may be allowed for both chroma block and            luma block, while in 4:2:0 chroma format, the horizontal TT            split may be allowed for luma block but disabled for chroma            block.        -   iv. In one example, for M×N (such as 32×4) coding tree node            with vertical TT split, in 4:2:2 chroma format, the vertical            TT split may be allowed for both chroma block and luma            block, while in 4:2:0 chroma format, the vertical TT split            may be allowed for luma block but disabled for chroma block.        -   v. In one example, for 4:0:0, and/or 4:4:4 color formats,            small block constraints may be not applied.    -   e. In one example, whether to enable SCIPU is dependent on the        color format.        -   i. In one example, SCIPU is enabled for 4:2:0 and 4:2:2            color formats.        -   ii. In one example, SCIPU is disabled for 4:0:0 and/or 4:4:4            color format.-   2. How to determine the prediction modes (and/or modeType) for    (sub-)blocks of a coding tree node may depend on chroma formats.    -   a. In one example, if one of the below conditions is true, the        modeType of (sub-)blocks partitioned by this coding tree node        may be equal to MODE_TYPE_ALL for 4:2:2 chroma format, while for        4:2:0 chroma format, the modeType may be equal to either        MODE_TYPE_INTRA or MODE_TYPE_INTER.        -   i. M×N (such as 8×8) coding tree node with horizontal BT            split        -   ii. M×N (such as 16×4) coding tree node with vertical BT            split        -   iii. M×N (such as 8×16) coding tree node with horizontal TT            split        -   iv. M×N (such as 32×4) coding tree node with vertical TT            split    -    For example, modeType may be set as MODE_TYPE_ALL for 4:2:2;        while modeType must be either MODE_TYPE_INTRA or MODE_TYPE_INTER        for 4:2:0, when one of the following conditions is true: i) luma        8×8 block with horizontal BT, ii) luma 16×4 block with vertical        BT, iii) luma 8×16 block with horizontal TT; iv) luma 32×4 block        with vertical TT.    -    Thus, for a block with three color components in a coding tree,        when one of the above conditions are true, the block for 4:2:0        is not categorized as MODE_TYPE_ALL (wherein all coding modes        can be selected). It is either MODE_TYPE_INTRA (wherein the        block can select palette, intra or intra block copy) or        MODE_TYPE_INTER (wherein only inter mode can be selected).-   3. Chroma intra (and/or IBC) blocks with block width equal to M    (such as M=2) chroma samples may be not allowed.    -   a. In one example, 2×N (such as N<=64)chroma intra blocks may be        not allowed in dual tree.        -   i. In one example, when treeType is equal to            DUAL_TREE_CHROMA and the block width is equal to 4 chroma            samples, vertical BT split may be disabled.        -   ii. In one example, when treeType is equal to            DUAL_TREE_CHROMA and the block width is equal to 8 chroma            samples, vertical TT split may be disabled.    -   b. In one example, 2×N (such as N<=64) chroma intra (and/or IBC)        blocks may be not allowed in single tree.        -   i. In one example, for M×N (such as M=8 and N<=64) coding            tree node with vertical BT split, one of below process may            be applied.            -   1. Vertical BT split may be disallowed for the 4×N or                4×(N/2) chroma block but allowed for the 8×N luma block.            -   2. The 4×N or 4×(N/2) chroma block may be not vertical                BT split, and it may be coded by MODE_INTRA, or                MODE_IBC.            -   3. Vertical BT split may be allowed for both the 8×N                luma block and the 4×N or 4×(N/2) chroma block, but both                luma and chroma blocks not coded by MODE_INTRA (e.g.,                may be coded by MODE_INTER, or MODE_IBC).        -   ii. In one example, for M×N (such as M=16 and N<=64) coding            tree node with vertical TT split, one of below process may            be applied.            -   1. Vertical TT split may be disallowed for the 8×N or                8×(N/2) chroma block but allowed for the 16×N luma                block.            -   2. The 8×N or 8×(N/2) chroma block may be not vertical                TT split and coded by MODE_INTRA, or MODE_IBC.            -   3. Vertical TT split may be allowed for both the 16×N                luma block and the 8×N or 8×(N/2) chroma block, but both                luma and chroma blocks may be not coded by MODE_INTRA                (e.g., may be coded by MODE_INTER, or MODE_IBC).-   4. IBC mode may be allowed for luma and/or chroma blocks regardless    of whether it is of small block size.    -   a. In one example, IBC mode may be allowed for luma blocks        including 8×4/8×8/16×4 and 4×N (such as N<=64) luma blocks, even        if modeType is equal to MODE_TYPE_INTRA.    -   b. In one example, IBC mode may be allowed for chroma blocks,        even if modeType is equal to MODE_TYPE_INTRA.-   5. The signaling of IBC prediction mode flag may depend on    prediction mode type (e.g., MODE_TYPE_INTRA).    -   a. In one example, IBC prediction mode flag for a non-SKIP block        (e.g. a coding block which is not coded by skip mode) may be        explicitly signaled in the bitstream when the treeType is not        equal to DUAL_TREE_CHROMA and the modeType is equal to        MODE_TYPE_INTRA.-   6. IBC prediction mode flag may be inferred depending on the CU SKIP    flag and the mode type (e.g., modeType).    -   a. In one example, if the current block is coded with SKIP mode        (such as cu_skip_flag is equal to 1), and the modeType is equal        to MODE_TYPE_INTRA, the IBC prediction mode flag (such as        pred_mode_ibc_flag) may be inferred to be equal to 1.-   7. The explicit signaling of Palette mode flag may not depend on the    modeType.    -   a. In one example, palette mode flag (such as        pred_mode_plt_flag) signaling may depend on the slice type,        block size, prediction mode, etc., But no matter what the        modeType is.    -   b. In one example, palette mode flag (such as        pred_mode_plt_flag) is inferred to be 0 when modeType is equal        to MODE_TYPE_INTER or MODE_TYPE_INTRA.-   8. IBC mode may be allowed to use when modeType is equal to    MODE_TYPE_INTER    -   a. In one example, chroma IBC may be disallowed when modeType is        equal to MODE_TYPE_INTRA.    -   b. In one example, IBC mode may be allowed to use when modeType        is equal to MODE_TYPE_INTRA or MODE_TYPE_INTER.    -   c. In one example, IBC mode may be allowed to use regardless        what modeType is.    -   d. In one example, within one SCIPU, IBC and inter mode may be        both allowed.    -   e. In one example, the size of IBC chroma block may always        corresponds to the size of corresponding luma block.    -   f. In one example, when modeType is equal to MODE_TYPE_INTER and        coding unit size is 4×4 in luma, signaling of pred_mode_ibc_flag        may be skipped and pred_mode_ibc_flag may be inferred to be        equal to 1.-   9. Palette mode may be allowed to use when modeType is    MODE_TYPE_INTER    -   a. In one example, chroma palette may be disallowed when        modeType is MODE_TYPE_INTRA.    -   b. In one example, palette mode may be allowed to use when        modeType is equal to MODE_TYPE_INTRA or MODE_TYPE_INTER.    -   c. In one example, palette mode may be allowed to use regardless        what modeType is.    -   d. In one example, within one SCIPU, palette and inter mode may        be both allowed.    -   e. In one example, within one SCIPU, palette, IBC and inter mode        may be all allowed.    -   f. In one example, the size of palette chroma block may always        corresponds to the size of corresponding luma block.    -   g. In one example, when modeType is equal to MODE_TYPE_INTER and        coding unit size is 4×4 in luma, signaling of pred_mode_plt_flag        may be skipped and pred_mode_plt_flag may be inferred to be        equal to 1.    -   h. In one example, when modeType is equal to MODE_TYPE_INTER and        coding unit size is 4×4 in luma, one message may be sent to        indicated if the current prediction mode is of IBC or palette.-   10. For small chroma blocks with width equal to M (e.g., M=2) or    height equal to N (e.g., N=2), allowed intra prediction modes may be    restricted to be different from those allowed for large chroma    blocks.    -   a. In one example, only a subset of intra prediction mode of        available chroma intra prediction modes may be used.    -   b. In one example, only INTRA_DC mode may be used.    -   c. In one example, only INTRA_PLANAR mode may be used.    -   d. In one example, only INTRA_ANGULAR18 mode may be used.    -   e. In one example, only INTRA_ANGULAR50 mode may be used.    -   f. In one example, CCLM modes may be disallowed.-   11. For small chroma blocks with width equal to M (e.g., M=2) or    height equal to N (e.g., N=2), transform types may be restricted to    be different from those allowed for large chroma blocks.    -   a. In one example, only transform skip may be used.    -   b. In one example, only one-dimensional transform may be used.    -   c. In one example, coding tools that support multiple types of        transforms are disallowed.        -   i. Alternatively, the signaling of coding tools that support            multiple types of transforms is omitted.-   12. CIIP may be considered as MODE_TYPE_INTRA.    -   a. In one example, CIIP mode may be allowed when dualtree        partitioning is used.        -   i. In one example, CIIP mode may be allowed when CU type is            of DUAL_TREEE_CHROMA.    -   b. Alternatively, CIIP may be considered as MODE_TYPE_INTER        -   i. In one example, when chroma block width is equal to M            (e.g., M=2), CIIP mode may be disallowed.        -   ii. In one example, when chroma block width is equal to M            (e.g., M=2), intra prediction modes for chroma in CIIP may            be restricted to simple intra prediction mode.            -   1. In one example, INTRA_DC may be used for chroma intra                prediction, when chroma block width is equal to M (e.g.,                M=2).            -   2. In one example, INTRA_ANGULAR18 may be used for                chroma intra prediction, when chroma block width is                equal to M (e.g., M=2).            -   3. In one example, INTRA_ANGULAR50 may be used for                chroma intra prediction, when chroma block width is                equal to M (e.g., M=2).        -   iii. In one example, intra prediction modes for chroma in            CIIP may be restricted to simple intra prediction mode.            -   1. In one example, INTRA_DC may be used for chroma intra                prediction.            -   2. In one example, INTRA_ANGULAR18 mode may be used for                chroma intra prediction.            -   3. In one example, INTRA_ANGULAR50 mode may be used for                chroma intra prediction.-   13. For above bullets, the variables M and/or N may be pre-defined    or signaled.    -   a. In one example, M and/or N may be further dependent on color        formats (e.g., 4:2:0, 4:2:2, 4:4:4).

5. Embodiments

Newly added parts are highlighted in bold and Italic, and the deletedparts from VVC working draft are marked with double brackets (e.g.,denotes the deletion of the character “a”). The modifications are basedon the latest VVC working draft (JVET-O2001-v11)

5.1 an Example Embodiment #1

The embodiment below is about the constraints on small block partitionsand prediction modes are applied to 4:2:0 and 4:4:4 chroma formats only(not apply to 4:0:0 and 4:4:4 chroma formats).

7.4.9.4 Coding Tree Semantics

The variable modeTypeCondition is derived as follows:

-   -   If one of the following conditions is true, modeTypeCondition is        set equal to 0        -   slice_type==I and qtbtt_dual_tree_intra_flag is equal to 1

        -   modeTypeCurr is not equal to MODE_TYPE_ALL

        -   

        -       -   Otherwise, if one of the following conditions is true,        modeTypeCondition is set equal to 1        -   cbWidth*cbHeight is equal to 64 and split_qt_flag is equal            to 1        -   cbWidth*cbHeight is equal to 64 and            MttSplitMode[x0][y0][mttDepth] is equal to SPLIT_TT_HOR or            SPLIT_TT_VER        -   cbWidth*cbHeight is equal to 32 and            MttSplitMode[x0][y0][mttDepth] is equal to SPLIT_BT_HOR or            SPLIT_BT_VER    -   Otherwise, if one of the following conditions is true,        modeTypeCondition is set equal to 1+(slice_type !=I? 1:0)        -   cbWidth*cbHeight is equal to 64 and            MttSplitMode[x0][y0][mttDepth] is equal to SPLIT_BT_HOR or            SPLIT_BT_VER        -   cbWidth*cbHeight is equal to 128 and            MttSplitMode[x0][y0][mttDepth] is equal to SPLIT_TT_HOR or            SPLIT_TT_VER    -   Otherwise, modeTypeCondition is set equal to 0

5.2 an Example Embodiment #2

The embodiment below is about the signaling of Palette mode flag notdepend on the mode Type.

7.3.8.5 Coding Unit Syntax

coding unit( x0, y0, cbWidth, cbHeight, cqtDepth, treeType, modeType) {Descriptor chType = treeType = = DUAL TREE CHROMA? 1: 0 if( slice type!= I | | sps_ibc_enabled_flag | | sps_palette enabled flag) { if(treeType != DUAL_TREE_CHROMA && !( ( ( cbWidth = = 4 && cbHeight = = 4)| | modeType = = MODE_TYPE_INTRA ) && !sps_ibc_enabled_flag ) )cu_skip_flag[ x0 ][ y0 ] ae(v) if( cu_skip_flag[ x0 ][ y0 ] = = 0 &&slice_type != I && !( cbWidth = =4 && cbHeight = = 4 ) && modeType = =MODE_TYPE_ALL ) pred_mode_flag ae(v) if( ( ( slice_type = = I &&cu_skip_flag[ x0 ][ y0 ] = =0 ) | | ( slice type != I && ( CuPredMode[chType ][ x0 ][ y0 ] != MODE_INTRA | | ( cbWidth = = 4 && cbHeight = = 4&& cu_skip_flag[ x0 ][ y0 ] = = 0 ) ) ) ) && cbWidth <=64 && cbHeight <=64 && modeType != MODE_TYPE_INTER && sps_ibc_enabled_flag && treeType !=DUAL_TREE_CHROMA ) pred_mode_ibc_flag ae(v) if( ( ( ( slice_type = = I || ( cbWidth = =4 && cbHeight = = 4 ) | | sps_ibc_enabled_flag ) &&CuPredMode[ x0 ][ y0 ] = = MODE_INTRA) | | ( slice type != I && !(cbWidth = = 4 && cbHeight = = 4) && !sps_ibc_enabled_flag && CuPredMode[x0 ][ y0 ]+ != MODE_INTRA ) ) && sps_palette_enabled_flag && cbWidth <=64 && cbHeight <= 64 && && cu_skip_flag[ x0 ][ y0 ] = =0 [[ && modeType!= MODE INTER ]]) pred_mode_plt_flag ae(v)

5.3 an Example Embodiment #3

The embodiment below is about the IBC prediction mode flag is inferreddepending on the CU SKIP flag and the modeType.

pred_mode_ibc_flag equal to 1 specifies that the current coding unit iscoded in IBC prediction mode. pred_mode_ibc_flag equal to 0 specifiesthat the current coding unit is not coded in IBC prediction mode.

When pred_mode_ibc_flag is not present, it is inferred as follows:

-   -   If cu_skip_flag[x0][y0] is equal to 1, and cbWidth is equal to        4, and cbHeight is equal to 4, pred_mode_ibc_flag is inferred to        be equal 1.

    -   Otherwise, if both cbWidth and cbHeight are equal to 128,        pred_mode_ibc_flag is inferred to be equal to 0.

    -   

    -   Otherwise, if modeType is equal to MODE_TYPE_INTER,        pred_mode_ibc_flag is inferred to be equal to 0.

    -   Otherwise, if treeType is equal to DUAL_TREE_CHROMA,        pred_mode_ibc_flag is inferred to be equal to 0.

    -   Otherwise, pred_mode_ibc_flag is inferred to be equal to the        value of sps_ibc_enabled_flag when decoding an I slice, and 0        when decoding a P or B slice, respectively.

When pred_mode_ibc_flag is equal to 1, the variableCuPredMode[chType][x][y] is set to be equal to MODE_IBC for x=x0 . . .x0+cbWidth−1 and y=y0 . . . y0+cbHeight−1.

5.4 an Example Embodiment #4

The embodiment below is about the signaling of IBC prediction mode flagdepend on MODE_TYPE_INTRA, and or IBC mode is allowed for luma blocksregardless of whether it is small block size.

7.3.8.5 Coding Unit Syntax

coding unit( x0, y0, cbWidth, cbHeight, cqtDepth, treeType, modeType ) {Descriptor chType = treeType = = DUAL_TREE_CHROMA? 1: 0 if( slice_type!= I | | sps_ibc_enabled_flag | | sps_palette_enabled_flag) { if(treeType != DUAL_TREE_CHROMA && !( ( ( cbWidth = = 4 && cbHeight = = 4)| | modeType = = MODE_TYPE_INTRA ) && !sps_ibc_enabled_flag ) )cu_skip_flag[ x0 ][ y0 ] ae(v) if( cu_skip_flag[ x0 ][y0 ] = = 0 &&slice type != I && !( cbWidth = =4 && cbHeight = = 4 ) && modeType = =MODE_TYPE_ALL ) pred_mode_flag ae(v) if( ( ( slice type = = I &&cu_skip_flag[ x0 ][ y0 ] = =0) | | ( slice type != I && ( CuPredMode[chType][ x0 ][ y0 ] != MODE_INTRA | |

( cbWidth = = 4 && cbHeight = = 4 && cu_skip_flag[ x0 ][ y0 ] = = 0 ) )) ) && cbWidth <=64 && cbHeight <= 64 && modeType != MODE_TYPE_INTER &&sps_ibc_enabled_flag && treeType != DUAL_TREE_CHROMA )pred_mode_ibc_flag ae(v)

5.5 an Example Embodiment #5

The embodiment below is about applying different intra blocksconstraints for 4:2:0 and 4:2:2 color formats.

7.4.9.4 Coding Tree Semantics

The variable modeTypeCondition is derived as follows:

-   -   If one of the following conditions is true, modeTypeCondition is        set equal to 0        -   slice_type==I and qtbtt_dual_tree_intra_flag is equal to 1        -   modeTypeCurr is not equal to MODE_TYPE_ALL    -   Otherwise, if one of the following conditions is true,        modeTypeCondition is set equal to 1        -   cbWidth*cbHeight is equal to 64 and split_qt_flag is equal            to 1        -   cbWidth*cbHeight is equal to 64 and            MttSplitMode[x0][y0][mttDepth] is equal to SPLIT_TT_HOR or            SPLIT_TT_VER        -   cbWidth*cbHeight is equal to 32 and            MttSplitMode[x0][y0][mttDepth] is equal to SPLIT_BT_HOR or            SPLIT_BT_VER    -   Otherwise, if one of the following conditions is true,        modeTypeCondition is set equal to 1+(slice_type !=I? 1:0)        -   cbWidth*cbHeight is equal to 64 and            MttSplitMode[x0][y0][mttDepth] is equal to SPLIT_BT_HOR or            SPLIT_BT_VER

        -   cbWidth*cbHeight is equal to 128 and            MttSplitMode[x0][y0][mttDepth] is equal to SPLIT_BT_HOR or            SPLIT_BT_VER

        -   

        -   

        -   

        -       -   Otherwise, modeTypeCondition is set equal to 0

5.6 an Example Embodiment #6

The embodiment below is about disallowing 2×N chroma intra blocks insingle tree.

7.4.9.4 Coding Tree Semantics

The variable modeTypeCondition is derived as follows:

-   -   If one of the following conditions is true, modeTypeCondition is        set equal to 0        -   slice_type==I and qtbtt dual_tree_intra_flag is equal to 1        -   modeTypeCurr is not equal to MODE_TYPE_ALL    -   Otherwise, if one of the following conditions is true,        modeTypeCondition is set equal to 1        -   cbWidth*cbHeight is equal to 64 and split qt_flag is equal            to 1        -   cbWidth*cbHeight is equal to 64 and            MttSplitMode[x0][y0][mttDepth] is equal to SPLIT_TT_HOR or            SPLIT_TT_VER        -   cbWidth*cbHeight is equal to 32 and            MttSplitMode[x0][y0][mttDepth] is equal to SPLIT_BT_HOR or            SPLIT_BT_VER    -   Otherwise, if one of the following conditions is true,        modeTypeCondition is set equal to 1+(slice_type !=I? 1:0)        -   cbWidth*cbHeight is equal to 64 and            MttSplitMode[x0][y0][mttDepth] is equal to SPLIT_BT_HOR or            SPLIT_BT_VER

        -   cbWidth*cbHeight is equal to 128 and            MttSplitMode[x0][y0][mttDepth] is equal to SPLIT_TT_HOR or            SPLIT_TT_VER

        -   

        -       -   Otherwise, modeTypeCondition is set equal to 0

5.7 an Example Embodiment #7

The embodiment below is about disallowing 2×N chroma intra blocks indual tree.

6.4.2 Allowed Binary Split Process

The variable allowBtSplit is derived as follows:

-   -   If one or more of the following conditions are true,        allowBtSplit is set equal to FALSE:        -   cb Size is less than or equal to MinBtSizeY

        -   cbWidth is greater than maxBtSize

        -   cbHeight is greater than maxBtSize

        -   mttDepth is greater than or equal to maxMttDepth

        -   treeType is equal to DUAL_TREE_CHROMA and            (cbWidth/SubWidthC)*(cbHeight/SubHeightC) is less than or            equal to 16

        -   

        -   treeType is equal to DUAL_TREE_CHROMA and modeType is equal            to MODE_TYPE_INTRA    -   . . .

6.4.3 Allowed Ternary Split Process

The variable allowTtSplit is derived as follows:

-   -   If one or more of the following conditions are true,        allowTtSplit is set equal to FALSE:        -   cb Size is less than or equal to 2*MinTtSizeY

        -   cbWidth is greater than Min(MaxTbSizeY, maxTtSize)

        -   cbHeight is greater than Min(MaxTbSizeY, maxTtSize)

        -   mttDepth is greater than or equal to maxMttDepth

        -   x0+cbWidth is greater than pic_width_in_luma_samples

        -   y0+cbHeight is greater than pic_height_in_luma_samples

        -   treeType is equal to DUAL_TREE_CHROMA and            (cbWidth/SubWidthC)*(cbHeight/SubHeightC) is less than or            equal to 32

        -   

        -   treeType is equal to DUAL_TREE_CHROMA and modeType is equal            to MODE_TYPE_INTRA    -   Otherwise, allowTtSplit is set equal to TRUE.

5.8 an Example Embodiment #8

The embodiment below is about enablingMODE_IBC for SCIPU chroma blocks.

7.3.8.5 Coding Unit Syntax

coding unit( x0, y0, cbWidth, cbHeight, cqtDepth, treeType, modeType ) {Descriptor chType = treeType = = DUAL_TREE_CHROMA? 1: 0 if( slice type!= I | | sps_ibc_enabled_flag | | sps_palette enabled flag) { if(treeType != DUAL_TREE_CHROMA && !( ( ( cbWidth = = 4 && cbHeight = = 4)| | modeType = = MODE_TYPE_INTRA) && !sps_ibc_enabled_flag ) )cu_skip_flag[ x0 ][ y0 ] ae(v) if( cu skip flag[ x0 ][ y0 ] = = 0 &&slice_type != I && !( cbWidth = =4 && cbHeight = = 4 ) && modeType = =MODE_TYPE_ALL ) pred_mode_flag ae(v) if( ( ( slice_type = = I &&cu_skip_flag[ x0 ][ y0 ] = =0) | | ( slice type != I && ( CuPredMode[chType ][ x0 ][ y0 ] != MODE_INTRA | |

|| ( cbWidth = = 4 && cbHeight = = 4 && cu_skip_flag[ x0 ][ y0 ] = = 0 )) ) ) && cbWidth <=64 && cbHeight <= 64 && modeType != MODE_TYPE_INTER&& sps_ibc_enabled_flag &&

 = =

 [[ treeType != DUAL_TREE_CHROMA]]) pred_mode_ibc_flag ae(v)

FIG. 17A is a block diagram of a video processing apparatus 1700. Theapparatus 1700 may be used to implement one or more of the methodsdescribed herein. The apparatus 1700 may be embodied in a smartphone,tablet, computer, Internet of Things (IoT) receiver, and so on. Theapparatus 1700 may include one or more processors 1702, one or morememories 1704 and video processing hardware 1706. The processor(s) 1702may be configured to implement one or more methods described in thepresent document. The memory (memories) 1704 may be used for storingdata and code used for implementing the methods and techniques describedherein. The video processing hardware 1706 may be used to implement, inhardware circuitry, some techniques described in the present document.In some embodiments, the hardware 1706 may be at least partially orcompletely included within the processor 1702, e.g., a graphicsco-processor.

FIG. 17B is another example of a block diagram of a video processingsystem in which disclosed techniques may be implemented. FIG. 17B is ablock diagram showing an example video processing system 1710 in whichvarious techniques disclosed herein may be implemented. Variousimplementations may include some or all of the components of the system1710. The system 1710 may include input 1712 for receiving videocontent. The video content may be received in a raw or uncompressedformat, e.g., 8 or 10 bit multi-component pixel values, or may be in acompressed or encoded format. The input 1712 may represent a networkinterface, a peripheral bus interface, or a storage interface. Examplesof network interface include wired interfaces such as Ethernet, passiveoptical network (PON), etc. and wireless interfaces such as Wi-Fi orcellular interfaces.

The system 1710 may include a coding component 1714 that may implementthe various coding or encoding methods described in the presentdocument. The coding component 1714 may reduce the average bitrate ofvideo from the input 1712 to the output of the coding component 1714 toproduce a coded representation of the video. The coding techniques aretherefore sometimes called video compression or video transcodingtechniques. The output of the coding component 1714 may be eitherstored, or transmitted via a communication connected, as represented bythe component 1716. The stored or communicated bitstream (or coded)representation of the video received at the input 1712 may be used bythe component 1718 for generating pixel values or displayable video thatis sent to a display interface 1720. The process of generatinguser-viewable video from the bitstream representation is sometimescalled video decompression. Furthermore, while certain video processingoperations are referred to as “coding” operations or tools, it will beappreciated that the coding tools or operations are used at an encoderand corresponding decoding tools or operations that reverse the resultsof the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface mayinclude universal serial bus (USB) or high definition multimediainterface (HIDMI) or Displayport, and so on. Examples of storageinterfaces include SATA (serial advanced technology attachment), PCI,IDE interface, and the like. The techniques described in the presentdocument may be embodied in various electronic devices such as mobilephones, laptops, smartphones or other devices that are capable ofperforming digital data processing and/or video display.

FIG. 18 is a flowchart for a method 1800 of processing a video. Themethod 1800 includes parsing (1802), for a conversion between a videoregion of a video and a coded representation of the video region, thecoded representation according to a syntax rule that defines arelationship between a chroma block size and a color format of the videoregion; and performing (1804) the conversion by performing the parsingaccording to the syntax rule.

FIG. 21A is a flowchart for a method 2110 of processing a video. Themethod 2110 includes, at step 2112, determining a partitioning schemefor partitioning a chroma video region of a video into one or morechroma blocks based on a color format of the video according to a rule.The method 2110 further includes, at step 2114, performing a conversionbetween the video and a coded representation of the video according tothe partitioning scheme.

FIG. 21B is a flowchart for a method 2120 of processing a video. Themethod 2120 includes, at step 2122, determining prediction modes orprediction types for subblocks of a coding tree node of a video based ona color format of the video. The method 2120 further includes, at step2124, performing a conversion between the video and a codedrepresentation of the video based on the determining. In someimplementations, the coding tree node is partitioned into the subblocksfor coding in the coded representation.

FIG. 22A is a flowchart for a method 2210 of processing a video. Themethod 2210 includes, at step 2212, performing a conversion between avideo and a coded representation of the video. In some implementations,the conversion is performed between the video comprising one or morevideo regions comprising one or more luma blocks and one or more chromaand the coded representation according to a rule, wherein the rulespecifies that a chroma block from the one or more chroma blocks havinga size M×N is disallowed to be represented in the coded representationusing an intra mode or an intra block copy mode, wherein M and N areintegers that indicate a width and a height of the chroma block,respectively, wherein the intra mode includes encoding the chroma blockbased on previously encoded or reconstructed video blocks, and whereinthe intra block copy mode includes encoding the chroma block using atleast a block vector pointing to a video frame containing a videoregion.

In some implementations, the conversion is performed between a chromablock of the video and the coded representation of the video, whereinthe chroma block is represented in the coded representation using anintra coding mode according to a size rule; wherein the size rulespecifies that the intra coding mode is from a first set of intra codingmode types, in case that a width of the chroma block is equal to M or aheight of the chroma block is equal to N, where M and N are integers;otherwise the intra coding mode is from a second set of intra codingmode types.

In some implementations, the conversion is performed between a chromablock of the video and a coded representation of the video, wherein thechroma block is represented in the coded representation using atransform type according to a rule, wherein the rule specifies that thetransform type is from a first set of transform types in case that awidth of the chroma block is equal to M or a height of the chroma blockis equal to N, where M and N are integers; otherwise the transform typeis from a second set of transform types.

In some implementations, the conversion is performed between the videocomprising a video region having one or more luma blocks and one or morechroma blocks and the coded representation of the video according to arule, wherein the rule specifies that use of an intra block copy (IBC)mode is available for the one or more luma blocks and the one or morechroma blocks having a block size M×N, for all values of M and N, whereM and N are integers; wherein, using the IBC mode, a video block iscoded using at least a block vector pointing to a video frame containingthe video block.

In some implementations, the conversion is performed between a videoblock of the video and the coded representation of the video block,wherein the coded representation conforms to a formatting rule, whereinthe formatting rule specifies a selective inclusion of a syntax elementindicative of use of an inter block copy (IBC) mode in the codedrepresentation based on a mode type of the video block, and wherein theIBC mode includes encoding the video block using at least a block vectorpointing to a video frame containing the video block.

In some implementations, the conversion is performed between a videoblock of the video and the coded representation of the video block,wherein the coded representation conforms to a formatting rule, whereinthe formatting rule specifies that a syntax element indicative of use ofa palette mode is included in the coded representation regardless of amode type of the video block, and wherein the pallet mode includesencoding the video block using a palette of representative samplevalues.

FIG. 22B is a flowchart for a method 2220 of processing a video. Themethod 2220 includes, at step 2222, determining, for a conversionbetween a video region of a video and a coded representation of thevideo, to use a combined inter and intra prediction (CIIP) mode as anintra mode or an inter mode according to a rule. The method 2220 furtherincludes, at step 2224, performing the conversion based on thedetermining. The CIIP mode include combining an intra prediction signaland a inter prediction signal using weighted coefficients.

FIG. 23A is a flowchart for a method 2310 of processing a video. Themethod 2310 includes, at step 2312, determining, for a conversionbetween a video region of a video and a coded representation of thevideo, based on a rule, that use of an inter block copy (IBC) mode ispermitted for the video region. The method 2310 further includes, atstep 2314, performing the conversion based on the determining. The IBCmode includes encoding the video region using at least a block vectorpointing to a video frame containing the video region.

FIG. 23B is a flowchart for a method 2320 of processing a video. Themethod 2320 includes, at step 2322, determining, for a conversionbetween a video region of a video and a coded representation of thevideo, based on a rule, whether use of a palette mode is permitted forthe video region. The method 2320 further includes, at step 2324,performing the conversion based on the determining. In someimplementations, the rule is based on a coding mode type of the videoregion or a color type of the video region, and wherein the palette modeincludes encoding the video region using a palette of representativesample values.

Some embodiments of the disclosed technology include making a decisionor determination to enable a video processing tool or mode. In anexample, when the video processing tool or mode is enabled, the encoderwill use or implement the tool or mode in the processing of a block ofvideo, but may not necessarily modify the resulting bitstream based onthe usage of the tool or mode. That is, a conversion from the block ofvideo to the bitstream representation of the video will use the videoprocessing tool or mode when it is enabled based on the decision ordetermination. In another example, when the video processing tool ormode is enabled, the decoder will process the bitstream with theknowledge that the bitstream has been modified based on the videoprocessing tool or mode. That is, a conversion from the bitstreamrepresentation of the video to the block of video will be performedusing the video processing tool or mode that was enabled based on thedecision or determination.

Some embodiments of the disclosed technology include making a decisionor determination to disable a video processing tool or mode. In anexample, when the video processing tool or mode is disabled, the encoderwill not use the tool or mode in the conversion of the block of video tothe bitstream representation of the video. In another example, when thevideo processing tool or mode is disabled, the decoder will process thebitstream with the knowledge that the bitstream has not been modifiedusing the video processing tool or mode that was disabled based on thedecision or determination.

In the present document, the term “video processing” may refer to videoencoding, video decoding, video compression or video decompression. Forexample, video compression algorithms may be applied during conversionfrom pixel representation of a video to a corresponding bitstreamrepresentation or vice versa. The bitstream representation of a currentvideo block may, for example, correspond to bits that are eitherco-located or spread in different places within the bitstream, as isdefined by the syntax. For example, a macroblock may be encoded in termsof transformed and coded error residual values and also using bits inheaders and other fields in the bitstream.

The following clauses describe some embodiments and techniques. Thefirst set of clauses describes certain features and aspects of thedisclosed techniques in the previous section.

1. A method of video processing, comprising: parsing, fora conversionbetween a video region of a video and a coded representation of thevideo region, the coded representation according to a syntax rule thatdefines a relationship between a chroma block size and a color format ofthe video region; and performing the conversion by performing theparsing according to the syntax rule.

2. The method of clause 1, wherein the color format is 4:4:4 and wherethe syntax rule specifies that the chroma block is subject to a samesize constraint as that for a luma blocks.

3. The method of clause 1, wherein the color format is 4:2:2 and wherethe syntax rule specifies that the chroma block is subject to a samesize constraint as that for 4:2:0 color format.

4. The method of any of clauses 1-3, wherein the syntax specifies that aprediction modes and small block partitions are used in a chroma-formatdependent manner.

5. The method of clause 1, wherein the syntax rule defines that asmallest allowed size feature is enabled for the conversion of the videoregion based on the color format of the video region.

The following clauses may be implemented together with additionaltechniques described in item 2 of the previous section.

6. A method of video processing, comprising: determining, based on aproperty of a video and a chroma format of the video, a coding mode of acoding tree node of the video; and performing a conversion between acoded representation of the video and a video block of the coding treenode using the determined coding mode.

7. The method of clause 6, wherein the coding mode is determined to beMODE_TYPE_ALL for the chroma format being 4:2:2, MODE_TYPE_INTRA orMODE_TYPE_INTER for the chroma format being 4:2:0 in case the propertyis:

i. the coding node is an M×N coding tree node with a horizontal binarytree split;

ii. the coding node is an M×N coding tree node with a vertical binarytree split;

iii. the coding node is an M×N coding tree node with a horizontalternary tree split; or

iv. the coding node is an M×N coding tree node with a vertical ternarytree split.

8. The method of clause 7, wherein M=8, or 16 or 32 and N=4 or 8 or 16.

The following clauses may be implemented together with additionaltechniques described in item 3 of the previous section.

9. A method of video processing, comprising: determining, based on arule, whether a certain size of chroma blocks is allowed in a videoregion of a video; and performing a conversion between the video regionand a coded representation of the video region based on the determining.

10. The method of clause 9, wherein the rule specifies that 2×N chromablocks are disallowed due to the video region including a dual treepartition.

11. The method of clause 9, wherein the rule specifies that 2N chromablocks are disallowed due to the video region including a single treepartition.

12. The method of clause 10 or 11, wherein N<=64.

The following clauses may be implemented together with additionaltechniques described in items 4, 8 and 9 of the previous section.

13. A method of video processing, comprising: determining, based on arule that allows use of a coding mode for a video condition, that acoding mode is permitted for a video region; and performing a conversionbetween a coded representation of pixels in the video region and pixelsof the video region based on the determining.

14. The method of clause 13, wherein the video condition is block size,and wherein the rule allows use of intra block copy mode for small blocksizes of luma blocks.

15. The method of clause 14, wherein the small block sizes include 8×4,8×8, 16×4 or 4×N luma block sizes.

16. The method of clause 13, wherein the rule allows use of intra blockcopy mode for conversion of the video region using a MODE_TYPE_INTERmode of coding.

17. The method of clause 13, wherein the rule allows use of palettecoding mode for conversion of the video region using a MODE_TYPE_INTERmode of coding.

The following clauses may be implemented together with additionaltechniques described in items 5, 6 and 7 of the previous section.

18. A method of video processing, comprising: performing a conversionbetween a video block of a video and a coded representation of the videoblock using a video coding mode, wherein a syntax element signaling thecoding mode is selectively included in the coded representation based ona rule.

19. The method of clause 18, wherein the video coding mode is an intrablock coding mode and wherein the rule specifies to use a type of thevideo coding mode to control inclusion of the syntax element in thecoded representation.

20. The method of clause 19, wherein the rule specifies explicitlysignaling a non-SKIP block.

21. The method of clause 18, wherein the rule specifies to implicitlysignal intra block copy flag based on a skip flag and a mode type of thevideo block.

22. The method of clause 18, wherein the coding mode is a palette codingmode and wherein the rule specifies to selectively include a palettecoding indicator based on mode type of the video block.

The following clauses may be implemented together with additionaltechniques described in item 11 of the previous section.

23. A method of video processing, comprising: determining, due to achroma block having a size less than a threshold size, that a transformtype used during a conversion between the chroma block and a codedrepresentation of the chroma block is different from a transform typeused for a corresponding luma block conversion; and performing theconversion based on the determining.

24. The method of clause 23, wherein the threshold size is M×N, whereinM is 2 or is 2.

The following clauses may be implemented together with additionaltechniques described in item 12 of the previous section.

25. The method of any of clauses 1 to 24 wherein, the conversion uses acombined inter and intra prediction mode as a MODE_TYPE_INTRA mode.

26. The method of any of clauses 18 to 22, wherein the conversion uses acombined inter and intra prediction mode as a MODE_TYPE_INTER mode. Forexample, when considering CIIP as MODE_TYPE_INTER, methods described initem 5+6+7 in the previous section may be applied. Or when methodsdescribed in items 5+6+7 are applied, CIIP can be considered asMODE_TYPE_INTER.

27. The method of any of clauses 1 to 26, wherein the conversioncomprises encoding the video into the coded representation.

28. The method of any of clauses 1 to 26, wherein the conversioncomprises decoding the coded representation to generate pixel values ofthe video.

29. A video decoding apparatus comprising a processor configured toimplement a method recited in one or more of clauses 1 to 28.

30. A video encoding apparatus comprising a processor configured toimplement a method recited in one or more of clauses 1 to 28.

3. A computer program product having computer code stored thereon, thecode, when executed by a processor, causes the processor to implement amethod recited in any of clauses 1 to 28.

32. A method, apparatus or system described in the present document.

The second set of clauses describes certain features and aspects of thedisclosed techniques in the previous section, for example, ExampleImplementations 1, 2, and 13.

1. A method of video processing, comprising: determining a partitioningscheme for partitioning a chroma video region of a video into one ormore chroma blocks based on a color format of the video according to arule; and performing a conversion between the video and a codedrepresentation of the video according to the partitioning scheme.

2. The method of clause 1, wherein the rule specifies for inter slice orintra slice with three color components represented with a same codingtree node.

3. The method of clause 1 or 2, wherein the rule specifies to use a samepartitioning scheme to a chroma block and a luma block for a 4:4:4 colorformat.

4. The method of clause 1 or 2, wherein the rule specifies to use a samepartitioning constrains for 4:2:0 and 4:2:2 color formats.

5. The method of clause 1 or 2, wherein the rule specifies not to applythe partitioning scheme and/or constraints on prediction modes for 4:0:0or 4:4:4 color format.

6. The method of any of clause 1 or 2, wherein the rule specifies thepartitioning scheme and/or prediction modes that are applied based onthe color format of the video.

7. The method of clause 6, wherein, for a M×N coding tree node with ahorizontal BT (binary tree) split or a horizontal TT (ternary tree)split, in a 4:2:2 color format, the horizontal BT split or thehorizontal TT split is allowed for both of a chroma block and a lumablock.

8. The method of clause 6, wherein, for a M×N coding tree node with ahorizontal BT (binary tree) split or a horizontal TT (ternary tree)split, in a 4:2:0 color format, the horizontal BT split or thehorizontal TT (ternary tree) split is allowed for a luma block but notallowed for a chroma block.

9. The method of clause 6, wherein, for a M×N coding tree node with avertical BT (binary tree) split or a vertical TT (ternary tree) split,in a 4:2:2 color format, the vertical BT split or the vertical TT splitis allowed for both of a chroma block and a luma block.

10. The method of clause 6, wherein, for a M×N coding tree node with avertical BT (binary tree) split or a vertical TT (ternary tree) split,in a 4:2:0 color format, the vertical BT split or the vertical TT(ternary tree) split is allowed for a luma block but not allowed for achroma block.

11. The method of any of clauses 7-10, wherein M and/or N is predefinedor signaled.

12. The method of clause 11, wherein M and/or N is dependent on thecolor format of the video region.

13. The method of clause 6, wherein the rule specifies not to apply thepartitioning scheme to 4:0:0 and/or 4:4:4 color format.

14. The method of clause 1, wherein the rule specifies that a smallestchroma intra prediction unit (SCIPU) defined to restrict a size of achroma block is enabled for the conversion based on the color format ofthe video.

15. The method of clause 14, wherein the smallest chroma intraprediction unit is allowed for 4:2:0 and/or 4:2:2 color format.

16. The method of clause 14, wherein smallest chroma intra predictionunit is disallowed for 4:0:0 and/or 4:4:4: color format.

17. A method of video processing, comprising: determining predictionmodes or prediction types for subblocks of a coding tree node of a videobased on a color format of the video; and performing a conversionbetween the video and a coded representation of the video based on thedetermining, wherein the coding tree node is partitioned into thesubblocks for coding in the coded representation.

18. The method of clause 17, wherein a prediction mode of a subblock isdetermined as MODE_TYPE_ALL indicating an applicability of an intercoding mode, an intra mode, a palette mode, and an intra block copymode, due to the color format being 4:2:2.

19. The method of clause 17, wherein a prediction mode of a subblock isdetermined to be either i) MODE_TYPE_INTER indicating an applicabilityof inter coding modes only or ii) MODE_TYPE_INTRA indicating anapplicability of an intra mode, a palette mode, and an intra block copymode due to the color format being 4:2:0.

20. The method of clause 18 or 19, wherein the inter coding modeincludes representing or reconstructing the video using a temporalcorrelation, the inter mode includes representing or reconstructing thevideo based on a previously processed video block, the palette modeincludes representing or reconstructing the video using a palette ofrepresentative sample values, or the intra block copy mode includesrepresenting or reconstructing the video using at least a block vectorpointing to a video frame.

21. The method of any one of clauses 18 to 20, wherein the coding treenode satisfies one of following conditions: i) the coding tree nodecorresponds to a 8×8 luma block with a horizontal binary tree split, ii)the coding tree node corresponds to a 16×4 luma block with a verticalbinary tree split, iii) the coding tree node corresponds to a 8×16 lumablock with a horizontal ternary tree split, or iv) the coding tree nodecorresponds to a 32×4 luma block with a vertical ternary tree split.

22. The method of clause 17, wherein the coding three node is an M×Ncoding tree node and M and/or N is predefined or signaled.

23. The method of clause 22, wherein M and/or N is dependent on thecolor format of the video.

24. The method of any of clauses 1 to 23, wherein the performing of theconversion includes generating the coded representation from the video.

25. The method of any of clauses 1 to 23, wherein the performing of theconversion includes generating the video from the coded representation.

26. A video processing apparatus comprising a processor configured toimplement a method recited in any one or more of clauses 1 to 25.

27. A computer readable medium storing program code that, when executed,causes a processor to implement a method recited in any one or more ofclauses 1 to 25.

The third set of clauses describes certain features and aspects of thedisclosed techniques in the previous section, for example, ExampleImplementations 3 and 10-13.

1. A method of video processing, comprising: performing a conversionbetween a video comprising one or more video regions comprising one ormore luma blocks and one or more chroma blocks and a codedrepresentation of the video according to a rule; wherein the rulespecifies that a chroma block from the one or more chroma blocks havinga size M×N is disallowed to be represented in the coded representationusing an intra mode or an intra block copy mode, wherein M and N areintegers that indicate a width and a height of the chroma block,respectively; wherein the intra mode includes encoding the chroma blockbased on previously encoded or reconstructed video blocks, and whereinthe intra block copy mode includes encoding the chroma block using atleast a block vector pointing to a video frame containing a videoregion.

2. The method of clause 1, wherein the rule specifies that the chromablocking having a size of 2×N is disallowed due to the video regionbeing partitioned as a dual tree partition.

3. The method of clause 2, wherein the rule specifies that a vertical BT(binary tree) split is disabled for the chroma block in case that i) atree type of the chroma block is equal to a dual tree type and ii) M isequal to 4 chroma samples.

4. The method of clause 2, wherein the rule specifies that a vertical TT(ternary tree) split is disabled for the chroma block in case that i) atree type of the chroma block is equal to a dual tree type and ii) M isequal to 8 chroma samples

5. The method of clause 1, wherein the rule specifies that the chromablock having a size of 2×N is disallowed due to the video region beingpartitioned as a single tree partition.

6. The method of clause 5, wherein, for a M×N coding tree node with avertical BT (binary tree) split, the vertical BT split is disallowed forthe chroma block having a size of 4×N or 4×(N/2) but allowed for a lumablock having a size of 8×N.

7. The method of clause 5, wherein for a M×N coding tree node with avertical BT (binary tree) split, the vertical BT split is disallowed forthe chroma block having a size of 4×N or 4×(N/2).

8. The method of clause 5, wherein, for a M×N coding tree node with avertical BT (binary tree) split, the vertical BT split is allowed forthe chroma block having a size of 4×N or 4×(N/2) and a luma block havinga size of 8×N, and wherein the chroma block and the luma block are notcoded with the intra mode.

9. The method of clause 5, wherein, for a M×N coding tree node with avertical TT (ternary tree) split, the vertical TT split is disallowedfor the chroma block having a size of 8×N or 8×(N/2) but allowed for aluma block having a size of 16×N.

10. The method of clause 5, wherein for a M×N coding tree node with avertical TT (ternary tree) split, the vertical TT split is disallowedfor the chroma block having a size of 8×N or 8×(N/2).

11. The method of clause 5, wherein, for a M×N coding tree node with avertical TT (ternary tree) split, the vertical TT split is allowed forthe chroma block having a size of 8×N or 8×(N/2) and a luma block havinga size of 16×N, and wherein the chroma block and the luma block are notcoded with the intra mode.

12. A method of video processing, comprising: determining, for aconversion between a video region of a video and a coded representationof the video, to use a combined inter and intra prediction (CIIP) modeas an intra mode or an inter mode according to a rule; and performingthe conversion based on the determining, and wherein the CIIP modeinclude combining an intra prediction signal and a inter predictionsignal using weighted coefficients.

13. The method of clause 12, wherein the rule specifies to use the CIIPmode as the intra mode due to a dual tree partitioning used in the videoregion.

14. The method of clause 12, wherein the rule specifies to use the CIIPmode as the inter mode.

15. The method of clause 14, wherein the rule specifies to disable theCIIP mode due to a chroma block having a width equal to M.

16. The method of clause 12, wherein the rule specifies to restrictintra prediction modes for a chroma block coded with the CIIP mode tothe intra mode.

17. The method of clause 16, wherein the intra prediction modes includesan intra DC, intra_angular18 mode, or an intra_angular50 mode.

18. The method of clause 16, wherein the chroma block width is equal to2.

19. A method of video processing, comprising: performing a conversionbetween a chroma block of a video and a coded representation of thevideo, wherein the chroma block is represented in the codedrepresentation using an intra coding mode according to a size rule;wherein the size rule specifies that the intra coding mode is from afirst set of intra coding mode types, in case that a width of the chromablock is equal to M or a height of the chroma block is equal to N, whereM and N are integers; otherwise the intra coding mode is from a secondset of intra coding mode types.

20. The method of clause 19, wherein M=2 or N=2.

21. The method of clause 19 or 20, wherein the first set of intra codingmode types is a subset of all allowed intra coding mode types in theconversion.

22. The method of clause 19 or 20, wherein the first set of intra codingmode types corresponds to an INTRA_DC mode.

23. The method of clause 19 or 20, wherein the first set of intra codingmode types corresponds to an INTRA_PLANAR mode.

24. The method of clause 19 or 20, wherein the first set of intra codingmode types corresponds to an INTRA_ANGULAR18 mode.

25. The method of clause 19 or 20, wherein the first set of intra codingmode types corresponds to an INTRA_ANGULAR50 mode.

26. The method of clause 19 or 20, wherein the rule specifies that aCCLM mode that uses a linear mode to derive prediction values of achroma component from another component is disallowed.

27. A method of video processing, comprising: performing a conversionbetween a chroma block of a video and a coded representation of thevideo, wherein the chroma block is represented in the codedrepresentation using a transform type according to a rule; wherein therule specifies that the transform type is from a first set of transformtypes in case that a width of the chroma block is equal to M or a heightof the chroma block is equal to N, where M and N are integers; otherwisethe transform type is from a second set of transform types.

28. The method of clause 27, wherein M is 2 or N is 2.

29. The method of any one of clauses 1-11, 15, 19-28, wherein M and/or Nis predefined or signaled.

30. The method of clause 29, wherein M and/or N is dependent on a colorformat of the video region.

31. The method of any of clauses 1 to 30, wherein the conversionincludes encoding the video into the coded representation.

32. The method of any of clauses 1 to 30, wherein the conversionincludes decoding the coded representation to generate the video.

33. A video processing apparatus comprising a processor configured toimplement a method recited in any one or more of clauses 1 to 32.

34. A computer readable medium storing program code that, when executed,causes a processor to implement a method recited in any one or more ofclauses 1 to 32.

The fourth set of clauses describes certain features and aspects of thedisclosed techniques in the previous section, for example, ExampleImplementations 4-9 and 13.

1. A method of video processing, comprising: performing a conversionbetween a video comprising a video region having one or more luma blocksand one or more chroma blocks and a coded representation of the videoaccording to a rule, wherein the rule specifies that use of an intrablock copy (IBC) mode is available for the one or more luma blocks andthe one or more chroma blocks having a block size M×N, for all values ofM and N, where M and N are integers; wherein, using the IBC mode, avideo block is coded using at least a block vector pointing to a videoframe containing the video block.

2. The method of clause 1, wherein the rule specifies that a luma blockhas the size of 8×4, 8×8, 16×4, or 4×N.

3. The method of clause 2, wherein the luma block has a mode type thatis equal to MODE_TYPE_INTRA indicating an applicability of an intramode, the IBC mode and a palette mode.

4. The method of clause 1, wherein the rule specifies that a chromablock has a mode type that is equal to MODE_TYPE_INTRA indicating anapplicability of an intra mode, the IBC mode and a palette mode.

5. A method of video processing, comprising: performing a conversionbetween a video block of a video and a coded representation of the videoblock, wherein the coded representation conforms to a formatting rule,wherein the formatting rule specifies a selective inclusion of a syntaxelement indicative of use of an inter block copy (IBC) mode in the codedrepresentation based on a mode type of the video block, and wherein theIBC mode includes encoding the video block using at least a block vectorpointing to a video frame containing the video block.

6. The method of clause 5, wherein the formatting rule specifies toexplicitly signal the syntax element for the video block not coded witha skip mode in case that a tree type of the video block is not equal toDUAL_TREE_CHROMA and that the mode type of the video block is equal tothe MODE_TYPE_INTRA indicating an applicability of an intra mode, theIBC mode, and a palette mode.

7. The method of clause 5, wherein the formatting rule specifies toinfer the syntax element based on a skip flag and a mode type of thevideo block.

8. The method of clause 7, wherein the formatting rule specifies thatthe syntax element is inferred to be equal to 1 for the video blockcoded with a skip mode in case that the mode type of the video block isequal to the MODE_TYPE_INTRA indicating an applicability of an intramode, the IBC mode, and a palette mode.

9. A method of video processing, comprising: performing a conversionbetween a video block of a video and a coded representation of the videoblock, wherein the coded representation conforms to a formatting rule,wherein the formatting rule specifies that a syntax element indicativeof use of a palette mode is included in the coded representationregardless of a mode type of the video block, and wherein the palletmode includes encoding the video block using a palette of representativesample values.

10. The method of clause 9, wherein the formatting rule specifies theexplicit signaling based on at least one of a slice type, a block size,or a prediction mode of the video block.

11. The method of clause 9, wherein the formatting rule specifies thatthe syntax element is inferred to be equal to 0 in case that the modetype of the video block is equal to the MODE_TYPE_INTER indicating anapplicability of an inter coding mode only or the MODE_TYPE_INTRAindicating an applicability of an intra mode, the IBC mode, and apalette mode.

12. A method of video processing, comprising: determining, for aconversion between a video region of a video and a coded representationof the video, based on a rule, that use of an inter block copy (IBC)mode is permitted for the video region; and performing the conversionbased on the determining, wherein the IBC mode includes encoding thevideo region using at least a block vector pointing to a video framecontaining the video region.

13. The method of clause 12, wherein the rule specifies that the IBCmode is allowed in case that a mode type of the video region is equal toMODE_TYPE_INTER indicating an applicability of an inter coding modeonly.

14. The method of clause 12, wherein the rule specifies that the IBCmode is not allowed for a chroma block in case that the mode type of thevideo region is equal to MODE_TYPE INTRA indicating an applicability ofan intra mode, the IBC mode, and a palette mode.

15. The method of clause 12, wherein the rule specifies that the IBCmode is allowed in case that the mode type is equal to MODE_TYPE INTERindicating an applicability of an inter coding mode only or MODE_TYPEINTRA indicating an applicability of an intra mode, the IBC mode, and apalette mode.

16. The method of clause 12, wherein the rule specifies that IBC mode isallowed independently of a mode type of the video region.

17. The method of clause 12, wherein the IBC mode and an inter mode areallowed within a smallest chroma intra prediction unit (SCIPU) definedto restrict a size of a chroma block.

18. The method of clause 12, wherein a chroma block coded using the IBCmode has a size corresponding to a size of a luma block corresponding tothe chroma block.

19. The method of clause 12, wherein signaling of a syntax elementindicative of use of the IBC mode is skipped and the syntax element isinferred to be equal to 1 in case that a mode type of the video regionequals to MODE_TYPE INTER indicating an applicability of an inter codingmode only and that the video region corresponds to a 4×4 luma block.

20. A method of video processing, comprising: determining, for aconversion between a video region of a video and a coded representationof the video, based on a rule, whether use of a palette mode ispermitted for the video region; and performing the conversion based onthe determining, wherein the rule is based on a coding mode type of thevideo region or a color type of the video region; wherein the palettemode includes encoding the video region using a palette ofrepresentative sample values.

21. The method of clause 20, the rule specifies that the palette mode isallowed in case that a mode type of the video region is equal toMODE_TYPE_INTER indicating an applicability of an inter coding modeonly.

22. The method of clause 20, wherein the rule specifies that the palettemode is not allowed fora chroma block in case that the mode type of thevideo region is equal to MODE_TYPE INTRA indicating an applicability ofan intra mode, an IBC mode, and a palette mode, and wherein the IBC modeincludes encoding the video region using at least a block vectorpointing to a video frame containing the video region.

23. The method of clause 20, wherein the rule specifies that the palettemode is allowed in case that the mode type is equal to MODE_TYPE INTERindicating an applicability of an inter coding mode only or MODE_TYPEINTRA indicating an applicability of an intra mode, an IBC mode, and apalette mode, and wherein the IBC mode includes encoding the videoregion using at least a block vector pointing to a video framecontaining the video region.

24. The method of clause 20, wherein the rule specifies that the palettemode is allowed independently of a mode type of the video region.

25. The method of clause 20, wherein the palette mode and an inter modeare allowed within a smallest chroma intra prediction unit (SCIPU)defined to restrict a size of a chroma block.

26. The method of clause 20, wherein all of the palette mode, an IBCmode, and an inter mode are allowed within a smallest chroma intraprediction unit (SCIPU) defined to restrict a size of a chroma block,the IBC mode includes encoding the video region using at least a blockvector pointing to a video frame containing the video region.

27. The method of clause 20, wherein a chroma block coded using thepalette mode has a size corresponding to a size of a luma blockcorresponding to the chroma block.

28. The method of clause 20, wherein signaling of a syntax elementindicative of use of the palette mode is skipped and the syntax elementis inferred to be equal to 1 in case that a mode type of the videoregion equals to MODE_TYPE INTER indicating an applicability of an intercoding mode only and that the video region corresponds to a 4×4 lumablock.

29. The method of clause 20, wherein a syntax element indicating of useof the palette mode or an IBC mode is included in the codedrepresentation in case that 1) a mode type of the video region equals toMODE_TYPE INTER indicating an applicability of an inter coding modeonly, 2) the video region corresponds to a 4×4 luma block, and whereinthe IBC mode includes encoding the video region using at least a blockvector pointing to a video frame containing the video region.

30. The method of any one of clauses 1-4, wherein M and/or N ispredefined or signaled.

31. The method of clause 30, wherein M and/or N is dependent on a colorformat of the video region.

32. The method of any of clauses 1 to 31, wherein the performing of theconversion includes generating the coded representation from the video.

33. The method of any of clauses 1 to 31, wherein the performing of theconversion includes generating the video from the coded representation.

34. A video processing apparatus comprising a processor configured toimplement a method recited in any one or more of clauses 1 to 33.

35. A computer readable medium storing program code that, when executed,causes a processor to implement a method recited in any one or more ofclauses 1 to 33.

The disclosed and other solutions, examples, embodiments, modules andthe functional operations described in this document can be implementedin digital electronic circuitry, or in computer software, firmware, orhardware, including the structures disclosed in this document and theirstructural equivalents, or in combinations of one or more of them. Thedisclosed and other embodiments can be implemented as one or morecomputer program products, i.e., one or more modules of computer programinstructions encoded on a computer readable medium for execution by, orto control the operation of, data processing apparatus. The computerreadable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more them. The term “data processing apparatus” encompassesall apparatus, devices, and machines for processing data, including byway of example a programmable processor, a computer, or multipleprocessors or computers. The apparatus can include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them. A propagated signal is anartificially generated signal, e.g., a machine-generated electrical,optical, or electromagnetic signal, that is generated to encodeinformation for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this document can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random-access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of non-volatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks;magneto optical disks; and CD ROM and DVD-ROM disks. The processor andthe memory can be supplemented by, or incorporated in, special purposelogic circuitry.

While this patent document contains many specifics, these should notbeconstrued as limitations on the scope of any subject matter or of whatmay be claimed, but rather as descriptions of features that may bespecific to particular embodiments of particular techniques. Certainfeatures that are described in this patent document in the context ofseparate embodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A method for processing video data, comprising:determining, for a conversion between a coding tree node of a video anda bitstream of the video, a scheme for splitting a luma parent block ofthe coding tree node and a chroma parent block of the coding tree node,and for predicting one or more luma blocks from the luma parent blockand one or more chroma blocks from the chroma parent block; andperforming the conversion according to the scheme, wherein a firstscheme is applied to the coding tree node for a first color format, andwherein a second scheme different from the first scheme is applied tothe coding tree node for a second color format different from the firstcolor format in case that the coding tree node satisfies a predeterminedcondition relating to a size of the luma parent block, and wherein inthe second scheme, for a coding tree node with a slice type being Islice, with a 4:2:0 color format and with a luma parent block having apredetermined size M×N, the luma parent block is allowed to be split totwo or more luma blocks with a horizontal BT (binary tree) partition ora vertical BT partition, and the chroma parent block of the coding treenode is not allowed to be split with the horizontal BT partition or thevertical BT partition, wherein the mode type of the two or more lumablocks are set to MODE_TYPE_INTRA or MODE_TYPE_INTER, and wherein M andN are positive integers.
 2. The method of claim 1, wherein the firstcolor format is 4:0:0 color format or 4:4:4 color format, and the secondcolor format is the 4:2:0 color format or 4:2:2 color format.
 3. Themethod of claim 2, wherein the first scheme and the second scheme havedifferent constrains on mode types of the one or more luma blocks andthe one or more chroma blocks.
 4. The method of claim 2, wherein in thefirst scheme, the mode types of the one or more luma blocks and the oneor more chroma blocks are MODE_TYPE_ALL, and wherein in the secondscheme, the mode types of the one or more luma blocks and the one ormore chroma blocks are MODE_TYPE_INTRA or MODE_TYPE_INTER.
 5. The methodof claim 2, wherein in the first scheme, a same partitioning scheme isused to partition the chroma parent block and the luma parent block, andwherein in the second scheme, in case that the mode type of the chromaparent block is MODE_TYPE_INTRA, different partitioning schemes are usedto partition the chroma parent block and the luma parent blockseparately.
 6. The method of claim 5, wherein in the second scheme, thechroma parent block is not allowed to be partitioned, and a tree type ofthe chroma parent block is set to DUAL_TREE_CHROMA.
 7. The method ofclaim 2, wherein in the second scheme, in case that a mode type of thechroma parent block is MODE_TYPE_INTRA, constrains on a size of thechroma parent block are same for the 4:2:0 color format and 4:2:2 colorformat, wherein the constrains comprise that at least one of a width anda height of the chroma parent block are both no less than
 4. 8. Themethod of claim 1, wherein the predetermined condition further relatesto a partition type of the luma parent block.
 9. The method of claim 1,wherein in the second scheme, for a coding tree node with a slice typebeing I slice, with a 4:2:2 color format and with a luma parent blockhaving the predetermined size M×N, the luma parent block and a chromaparent block of the coding tree node are both allowed to be split to twoor more luma blocks and two or more chroma blocks with the horizontal BTpartition or the vertical BT partition, wherein the mode types of thetwo or more luma blocks and the two or more chroma blocks are set toMODE_TYPE_ALL.
 10. The method of claim 9, wherein M×N=64.
 11. The methodof claim 8, wherein in the second scheme, for a coding tree node withthe slice type being I slice, with the 4:2:0 color format and with aluma parent block having a predetermined size M×N, the luma parent blockis allowed to be split to two or more luma blocks with a horizontal TT(ternary tree) partition or a vertical TT partition, and the chromaparent block of the coding tree node is not allowed to be split with thehorizontal TT partition or the vertical TT partition, wherein the modetypes of the two luma blocks and the chroma parent block are set toMODE_TYPE_INTRA or MODE_TYPE_INTER, and wherein M and N are positiveintegers.
 12. The method of claim 11, wherein in the second scheme, fora coding tree node with a slice type being I slice, with a 4:2:2 colorformat and with a luma parent block having the predetermined size M×N,the luma parent block and a chroma parent block of the coding tree nodeare both allowed to be split to two or more luma blocks and two or morechroma blocks with the horizontal TT partition or the vertical TTpartition, wherein the mode types of the two or more luma blocks and thetwo or more chroma blocks are set to MODE_TYPE_ALL.
 13. The method ofclaim 12, wherein M×N=128.
 14. The method of claim 1, wherein theconversion includes encoding the video into the bitstream.
 15. Themethod of claim 1, wherein the conversion includes decoding the videofrom the bitstream.
 16. An apparatus for processing video datacomprising a processor and a non-transitory memory with instructionsthereon, wherein the instructions upon execution by the processor, causethe processor to: determine, for a conversion between a coding tree nodeof a video and a bitstream of the video, a scheme for splitting a lumaparent block of the coding tree node into one or more luma blocks by oneor more partitions, for splitting a chroma parent block of the codingtree node into one or more chroma blocks by one or more partitions, andfor predicting the one or more luma blocks and the one or more chromablocks; and perform the conversion according to the scheme, wherein afirst scheme is applied to the coding tree node for a first colorformat, and wherein a second scheme different from the first scheme isapplied to the coding tree node for a second color format different fromthe first color format in case that the coding tree node satisfies apredetermined condition relating to a size of the luma parent block, andwherein in the second scheme, for a coding tree node with a slice typebeing I slice, with a 4:2:0 color format and with a luma parent blockhaving a predetermined size M×N, the luma parent block is allowed to besplit to two or more luma blocks with a horizontal BT (binary tree)partition or a vertical BT partition, and the chroma parent block of thecoding tree node is not allowed to be split with the horizontal BTpartition or the vertical BT partition, wherein the mode type of the twoor more luma blocks are set to MODE_TYPE_INTRA or MODE_TYPE_INTER, andwherein M and N are positive integers.
 17. The apparatus of claim 16,wherein the first color format is 4:0:0 color format or 4:4:4 colorformat, and the second color format is the 4:2:0 color format or 4:2:2color format.
 18. A non-transitory computer-readable storage mediumstoring instructions that cause a processor to: determine, for aconversion between a coding tree node of a video and a bitstream of thevideo, a scheme for splitting a luma parent block of the coding treenode into one or more luma blocks by one or more partitions, forsplitting a chroma parent block of the coding tree node into one or morechroma blocks by one or more partitions, and for predicting the one ormore luma blocks and the one or more chroma blocks; and perform theconversion according to the scheme, wherein a first scheme is applied tothe coding tree node for a first color format, and wherein a secondscheme different from the first scheme is applied to the coding treenode for a second color format different from the first color format incase that the coding tree node satisfies a predetermined conditionrelating to a size of the luma parent block, and wherein in the secondscheme, for a coding tree node with a slice type being I slice, with a4:2:0 color format and with a luma parent block having a predeterminedsize M×N, the luma parent block is allowed to be split to two or moreluma blocks with a horizontal BT (binary tree) partition or a verticalBT partition, and the chroma parent block of the coding tree node is notallowed to be split with the horizontal BT partition or the vertical BTpartition, wherein the mode type of the two or more luma blocks are setto MODE_TYPE_INTRA or MODE_TYPE_INTER, and wherein M and N are positiveintegers.
 19. A non-transitory computer-readable recording mediumstoring a bitstream of a video which is generated by a method performedby a video processing apparatus, wherein the method comprises:determining, for a coding tree node of a video, a scheme for splitting aluma parent block of the coding tree node into one or more luma blocksby one or more partitions, for splitting a chroma parent block of thecoding tree node into one or more chroma blocks by one or morepartitions, and for predicting the one or more luma blocks and the oneor more chroma blocks; and generating the bitstream according to thescheme, wherein a first scheme is applied to the coding tree node for afirst color format, and wherein a second scheme different from the firstscheme is applied to the coding tree node for a second color formatdifferent from the first color format in case that the coding tree nodesatisfies a predetermined condition relating to a size of the lumaparent block, and wherein in the second scheme, for a coding tree nodewith a slice type being I slice, with a 4:2:0 color format and with aluma parent block having a predetermined size M×N, the luma parent blockis allowed to be split to two or more luma blocks with a horizontal BT(binary tree) partition or a vertical BT partition, and the chromaparent block of the coding tree node is not allowed to be split with thehorizontal BT partition or the vertical BT partition, wherein the modetype of the two or more luma blocks are set to MODE_TYPE_INTRA orMODE_TYPE_INTER, and wherein M and N are positive integers.